Ask HN: Who here has built a profitable startup while keeping their day job?

261 points by jobsandjobs ↗ HN

192 comments

[ 3.1 ms ] story [ 243 ms ] thread
Based on my experience, I think it is a extremely difficult thing to do!
Not me - but, I think one of the prime examples is Warby Parker. At least according to 'Originals' by Adam Grant.

Mr. Grant scoffed at the founders meekness at not going full ahead and passed an opportunity to invest. After WP became successful Mr. Grant realized he had no idea how to gauge peoples tendency to succeed - which prompted him to write the book. Which is an excellent read.

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Sort of, I consulted in the day time and built my company in the evenings, after 3-4 years I switched to full time on my company, 6 years after that I made an exit.

While it worked for me, it came at a cost and I did not have a family at the time or any other obligations.

Tread carefully. If you’re going to do this, read your current employment agreement carefully especially the parts about Intellectual Property. Every medium-to-large company I have worked at has asserted ownership of everything I build, at work or away from work, using my own equipment, on my own time—it doesn't matter. If your employer can imagne a conflict of interest (for example could what you are working on potentially compete with a current or future business of your employer’s?), you’re screwed. I’ve had to end involvement with open source projects and home hobby projects because of the IP threats in my employment agreements. Feel free to take the risk yourself, personally I don’t feel like fighting a room full of corporate lawyers.

EDIT: jobsandjobs, sorry to have derailed your good Ask HN question but I thought this was an important and often-overlooked pitfall that people should be aware of.

Put it in your contract before you get employed. If starting a company while employed, reach out to your employer saying you're building company X which does Y as a side project and you need a document stating no IP ownership.
Sure you will be get hired while building a company.
I've hired 100+ engineers in my career. The ones with side projects are the best engineers. That said, sure I've had to fire some who don't perform.
Pretty common question to ask from hiring managers. It shows passion. Passion is a way better predictor of your work quality and commitment than asking ICPC whiteboard questions.
Side projects prove the passion, I certainly agree. Only, I can't get my head around if employee decides to start dreaming his/her side project taking over the current job. If odds are close and side project has good traction, maybe it's not ethical to work in fulltime before understanding it either.
It's not ethical to take a job you think you might leave at some point in the future? lol
Isn't fulltime an accepted life-style? I see lot of people didn't think far enough but loved their job. Indeed, they seem much happier than lost people in startups. If I would hire someone, I would like to work with that type of person. They can change their mind later, no problem.
No employer I have ever worked for would even consider modifying this language in their agreement. They are going to have a standard boilerplate and if you try to negotiate or modify it they will tell you “sign it unmodified or GTFO.” Ask me how I know :-)
My last two companies have modified their language.
Yeah, I request changes from both clients and W2 jobs and get most of what I want as well.
Counter anecdata: Many employers are happily willing to provide such carve-outs for ownership of side projects done at home on the employee’s own time and equipment.
This is interesting. Has this been your personal experience? If so, to what the extent?
I got my last employer to agree to change the IP terms. It was a typo in their document nobody caught, that asserted ownership on everything. They were only too happy to fix it so it only applied to work done for them. I did have an industry specific non-compete as well, but it's a fairly narrow segment, so I had no problem signing.

My current employment agreement specifically states I can run whatever enterprise I want outside of work so long as it doesn't interfere with my duties (and presumably their business).

I can confirm that. Two of the top 5 US tech companies told me to sign it as-is or GTFO.
At my first ever job, where I was among the first developers after the founders, they got such standard boilerplate template.

I asked them to remove that line and some others, and they did without discussion or trying to pressure me into signing.

They didn't actually notice the line being there when they downloaded it from the internet and it was consequently removed for future contracts.

This is not my experience, including early in my career when I worked for FedEx.
I know people who have had this part of their agreement removed
My ex-boss had an offer rescinded when he declared his personal IP on the form provided by the company. He had told interviewers about his significant IP/projects. Interviewers thought that was no problem.

On the first day of his job, he filled out a form declaring his current IP. Some HR/lawyer reviewed it and a week later he was let go. No real reason was given. But he spent his first week answering questions related to his projects, so it is pretty obvious they were worried about it.

Does anyone know how this works if you build a consulting business, or build software, but then don't claim any of the IP?
Not a lawyer, but you wouldn't be able to legally assign the IP from you to your client, as the IP would be owned by your employer.
> [...] or away from work, using my own equipment, on my own time [...]

That sounds illegal.

It is illegal in California
And Washington State. But actually some states (Montana comes to mind) have laws that can restrict you to one employer at a time.
It is legal in California if the company can show a conflict of interest.
Even if it is totally illegal, you're still going to go to court to fight it, and lawyers are expensive. Nobody sane is going to spend 30k+ going to trial on a side project.
On the flip side, no sane company is going to sue a former (or current) employee for IP ownership over work they did in their off hours - especially if it isn't directly related to the company's own business.
They could file the suit and then drop it last second. Most large companies have several lawyers on staff, so it's not really any additional cost.
Sure, they could, but they could do that whether or not there's verbiage about it in your contract. This is a problem with balance of power between large corporations and individuals, not with the contract conditions.
"asserted ownership of everything I build, at work or away from work, using my own equipment, on my own time—it doesn't matter"

That's the most ridiculous thing I've ever heard. Assuming you're not stealing technology, or doing it on their time or machines, there is no way a court would uphold that. If I build a house, or rebuild a car in my off time, they own that too? Corporations don't own your entire life.

Sadly this is fairly commonplace in IP contracts. Though some companies provide potential hires with an option to list "own inventions" wherein he/she can list projects they may continue to develop in their own time and retain ownership of. Granted, all entries therein are subject to approval by the company - obviously they won't let you pursue a project that is actually in competition with their business.
My understanding of the “list all inventions/projects” activity is that its purpose is to let the employer know what past projects they can’t grab, but it is not a way for you to continue working on them while still owning the IP. Their lawyers will say, “we can’t go after the parts of this project that were disclosed to us, but we can go after it based on the parts you’ve worked on since joining us.”
One of the many things that attracted me to my current company is that the employment contract specifically states that you own your stuff that you do on your own time, that doesn’t compete with the company, as long as you use your own equipment. Not really a problem for me since I have no creative ideas to start a business outside of generic cloud consulting and screening potential employees for other companies.
Even the grand old red state I'm working in doesn't allow these claims but it sure didn't stop the company I work for from asking me to agree to them.

After I moved and started working.

I made a small stink about it but they were adamant and eventually I caved. These laws are important.

Yep, I now ask to see these agreements before signing a job offer after making a similar mistake at a previous company.
I did too, and they made verbal promises that they went back on. Next time I'll make sure to ask in an on-the-record communications medium.
Oh, wow. Nice to start off a working relationship by lying to the new hire. I might have signed if I were in a financial bind (e.g., just moved cross-country and couldn't afford to be unemployed), but I would immediately start looking for another job.
Same here. Was working on some research projects and the future employer's recruiter said my new manager loves giving back and while I would have to reduce my hours on the project it should be fine. Legal did not agree, minor he-said-she-said spat and I reneged on the offer. I hate feeling like I'm an indentured servant for a company that wasn't even willing to match my existing pay.
This blog post has a decent explanation of the rationale for why they are written that way: https://www.joelonsoftware.com/2016/12/09/developers-side-pr...
I understand their rationale, but the problem is that unless your state protects you from nonsense, they are still written in a way where they literally are saying they own everything you do outside of the job. Likely? Who knows. But if an employer was really interested in the value of one of your projects, they could potentially bring up a suit against you for it.
It doesn't stop them from suing you though. Do you really want to deal with this stuff in court?

Anything I do in my private life I keep on the down low.

It also depends on where you live. It is illegal for an employer to do this in California. But just be sure to always do your side work on your own time and your own equipment.
I don't understand this how the hell would they even know what you are doing at home?

If your home project gains a little traction to financially support you then you quit the day job, and don't tell them anything. If not then it's some private home project you do.

Can't believe you are making decisions on what you do at home based on some company that could easily disappear, lay you off, get sold, etc etc, before your side projects ever materialize.

Absurd!

You can bet any decent sized company will have people keeping an eye out on ex-employees whose home projects miraculously gain WhatsApp-levels of traction. If you look to take on VC funding, I guarantee during the DD process they will ask you if you built any of the product while employed elsewhere, and if so, they’ll want to see your old employment agreement.
> whose home projects miraculously gain WhatsApp-levels of traction

Surely there is some middle ground between a $22 billion dollar company and a lifestyle business that generates $500k-$1m a year in revenue. Also if your company is WhatsApp level pretty sure you can afford a team of $500 an hour lawyers.

Most likely if the company is 500-1m revenue then it is basically a tiny company that won't be on anyone's radar. Decent sized sellers on ebay/amazon can easily generate 500k-1m revenue and the vast majority of people never heard of those stores before.

Even if you are running a decent sized business, just don't be the face of the company. The purpose of business is to make money, not become "famous".

Depends where you live, this is illegal in California.
IANAL, but I believe at least in California, emmployers have no right to IP that is unrelated to work IP and developed on your personal time on a personal laptop. If it is in a contract it should be unenforcable.

The key here is having a clear demarcation between work and personal projects.

“Personal time” isn't a clearcut concept for non-hourly employees, and I'm pretty sure the “unrelated” but applies to job duties (which can be quite expansive) not just existing work IP.
Also NAL, but my understanding (even in CA) is it comes down to whether or not there is a conflict of interest. Say you work for Amazon and want to write software for controlling drones. Is there a conflict of interest? Does Amazon make drones? Maybe? Maybe they will? Do/will they use drones and purchase drone software? I’m already seeing dollar signs (legal fees) flying past my eyeballs here. Why would anyone risk that kind of legal exposure, even if they are “really sure” they are right?
In my experience, big companies have restrictions around moonlighting when your startup directly competes with their services/products, and assert ownership over things you work on using the company's resources, ie company computers/internet/time. So if your startup is not directly competing, and you're doing it on your own time/computer/internet, you should be good.
I would think that the first step would be talking with your employer. (I what you are working on is not related to your work)

It’s a great litmus year to see if your employer is a bully or not.

Last "day job" I had, I just negotiated and got it removed from the contract. (I argued I'd be sending them quite some literal kilograms of paperwork, and surely that wasn't to anyone's benefit) . I don't know how common it is, but even fairly large companies will often allow some negotiation here.

(I don't like the fact that people put these kinds of clauses in in the first place either, but at least you can often opt out, fwiw)

contract != law.

You can also put in "we own your kidneys and your first born child"

Just because it is in a contract, it doesn't mean it's enforceable.

I agree with your point that one should be aware of it, but to go as far as not creating an awesome company and living comfortably because it's "risky" is ridiculous.

One should not be chained to a corporation forever if chooses not to.

[EDIT]

Also to add more to my point, litigation CANNOT be avoided.

If an entity (a person or a corporation) wants to come after you, they will find a way to do it.

Running any kind of viable business requires legal work and protection. It would be foolish to think otherwise

If your side project grows enough that you have either massive traction, VC funding or a good amount of cash, you can easily fight these in court .

And even if you don't fully win, it can be dragged on for years and meanwhile your business can continue to grow.

So it's a none issue.

Good thing my child has invented everything I ever created!
There's a ton of shitty legal advice in this subthread (NOT this first comment, which at the core "read your agreement" is pretty good advice). Ignore the people downthread who are making specific assertions about what is and isn't enforceable in what state. Rather, follow the advice that sensible people always give in this situation:

!!!!! If there is serious money at stake, or a reasonable prospect of serious money at stake for you, use some of that money to pay a lawyer admitted in your jurisdiction and familiar with the law on IP agreements and nocompetes to look at the agreement and advise you. It really won't cost all that much for a consultation and a bit of contract reading just to see where you stand. Then make a decision. !!!!!

(Source: IAAL (law professor actually), though I don't currently practice and am almost certainly not admitted in your jurisdiction.)

Fully agree with this, as I pointed out down the thread.

It would be foolish to think you can run a business without legal protection.

That shouldn't prevent one from chasing their dreams though. I think OP's message paint a darker than necessary paint regarding this.

(Source Currently doing this with a lawyer as a cofounder)

Yea I feel bad that ”tread carefully and read your legal agreement” turned out to be so controversial that it derailed an otherwise interesting Ask HN :(
IANAL but I would ping WSGR, F&W, Orrick... and be sure first that they're not representing your current employer.

Definitely build things on your own equipment, using different technologies, on your own time and nowhere near said company.

In California, noncompetes are rarely enforceable... but again IANAL and do you own homework.

Might be easier to combine a day job with freelancing rather than having a startup.
I think it's even easier to combine freelancing with having a startup. That's what I've been doing.
It depends, serious freelancing often requires some kind availability/responsiveness within business hours which may be tough with full-time day job. Of course the same applies to any high touch customer startup too.
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Yes, I tried doing this for a while and it’s frustrating for everyone.
Bootstrapped https://artcall.org and trying to gain traction on https://ezzl.art while employed full time elsewhere.
FYI, I cannot scroll down on on artcall.org.
Oh strange, can’t reproduce. Are you on mobile or desktop? Browser?
I could reproduce on OS X, Desktop, using Google Chrome. Hope that helps!
Windows, Desktop, Firefox : no issues

Windows, Desktop, Chrome: Clicking the scroll bar works; mouse wheel, arrows, page up/page down do not.

Same for me on Chrome. There's a 'mousewheel' event listener attached to the window that is calling preventDefault()
This absolutely infuriates me to the point where I'm struggling to remain civil. My blood instantly began boiling after reading that sentence.

Why the @#$% does some web designer think it's a good idea to disable mousewheel scrolling?! What does this accomplish? What feature do you gain? What was the goal?

I just can't for the life of me grok what would be going through someone's brain when they decide "Hey, you know what would make this page better? Disabling scrolling with your mouse wheel!"

EDIT: Maybe the intent was to do something else, like implementing smooth scrolling in JavaScript, and it's not working properly. But if that's the case, the answer is that web devs need to stop trying to mess with scrolling. Implementations rarely work correctly in every browser and it just ruins the UX. Just stop messing with scrolling!

In this case it's a bug, as I'm not trying to 'disable' the mouse, but track scrolling and then make the menu 'stick' to the header when the user scrolls down the page. A common design pattern which increases usability quite a bit.
Haha. Step down a notch, pal
What do you possibly gain from this kind of rage? It's rude and makes for an extremely low quality comment.
It hits a nerve when a programmer or designer either tries to fix something that isn't broken and ends up making it even worse (Such as web pages that try to implement smooth scrolling), or removes functionality for the sake of simplicity and it lowers usability. Yeah, in this case it was a bug, but let's not pretend it doesn't happen deliberately sometimes.
Whether it hits a nerve or not, there are more productive ways to express that you don't agree with an implementation. You acted like a bully and that's completely unacceptable.
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Thanks all! Looks like it's Chrome (was able to reproduce there). Will fix when I'm not at work. ;)
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Not really a startup in the sense of a VC backed multi million dollar company but three working friends and me have bootstrapped a fitness websites with science based health advice, mostly free, to basically the largest fitness related website in the Netherlands. Currently employing people, which i think still sounds insane for a hobby project. https://www.fit.nl. 700.000 pageviews a month. App, 2 books, system for training and meal schedules etc. One now works full time as a lead/writer.

As a day job I'm a full time resident of orthopedic surgery. Busy days. I've done most of the programming of the website (custom theme on wordpress), product comparison engine and other custom pages. And server admin for discourse, mattermost etc

Some important findings:

- You have to care otherwise it becomes a chore. In this case it keeps people healthy. We give free advice that i think is pretty good, e.g on the forum, I love that part. The link with the day job is here. Lots of stuff i tell people during clinic hours applies here as well

- As its completely different it still feels like a hobby. Learning to do stuff is fun

- Clear separation of responsibility, do stuff you are efficient in

- A ticketing system for jobs, pick up stuff when you have time. Anybody can add to the ticket list but the list owner decides what comes first.

- Keeping the tickets bite sized. GIT to deploy, deploy often

- A time tracking system (Toggle) tracks time spent.

- Mattermost for private discussions and planning

- Meetups and fun activities to keep the group focused

- Managed main server (websynthesis) in case the website goes down and the other technical guy or me are unavailable. More expensive but less stress this way.

What inspired a doctor to code? I assume that must have an inspiring story
Not really. Picked it up as a child, loved programming and tinkering. Had to choose between computer science and medicine. There are actually lots of things in common, debugging complex systems, building a mental model, abstraction, looking up solutions based on certain hints. Orthopedics is a highly technical field, working with implants, computer surgery, imaging and such so its very useful. Programming trains your problem solving abilities. I really believe everybody should have the opportunity to learn to code.
Medical students are often the best students from many other faculties or programs in their undergrad that end up in 1 program.

An example of this is Bioware, a gaming company was started by doctors.

(While I understand passion is important and you won't make it far in either without it) Which profession would you suggest just "for the money"? Doctor or Software Engineer? Taking into the account the time and loans it takes to come online as a doctor, and the assuming the person is good enough to become a surgeon or code at FAANG? Great website btw, and so inspiring.
I' m not in the US, so no crazy salaries on both sides. The average doctor probably makes more but the best programmer makes way more than the best doctor. However with long hours, night shifts, pressure etc you have to enjoy what you do or burn out early.
>However with long hours, night shifts, pressure etc you have to enjoy what you do or burn out early

Is this about the doctor or the programmer?

In the Netherlands I wouldn't expect any night shifts, or long hours as a programmer.
I am moving from programming to medicine.

I am appaled that we can't ask a body to grow and the mechanism is not even fullly understood.

So, my reaearch includes making body grow organs, bones and other tissues just using an app.

Imagine growing from 5'10 to 6'5

If you are going to try to do this, working remote is the ideal situation. When working remote I save about 2 or so hours. Traffic, packing a lunch, office politics, getting dressed, eating breakfast vs. eating breakfast in front of the computer... etc.
My day job was steady consulting work, but I used that to provide stability while building a company my partners and I sold last year. It wasn't a huge exit (in truth my cut barely covered the extra hours I put into it over four years) and one of these days I'm going to have to write up the history of this project as a cautionary tale about all the mistakes you can make getting involved with a startup. But it was mildly profitable, and with better marketing we probably could have tripled our valuation on exit.
I have a finance career, plus I built CanadaPups.com. Very little maintenance and costs, but lots of fun to tinker and improve it as a hobby. Just letting it grow on its own as I'm kinda out of ideas of how to kick it up a notch - suggestions welcome!. https://canadapups.com
That's actually a very smooth website for a side project!
How did you get the first few customers to achieve enough critical mass to make website successful?
I needed traffic from the buy-side and sell-side.

On the sell side (breeders), I can just google for new customers! Many dog breeders have their own websites. I search for dog breeders and then contact them through their website (either their webform or their published emails).

On the buy-side (people looking for pets), I pay for google ads on certain keyword searches. As my website became more relevant, the cost of the ads dropped significantly and I started getting more organic searches. Getting buy-side is more difficult for me. Once you find your new pet, you don't need to visit my website anymore, so customer retention is bad... something I need to work on.

Maybe curated lists or targeted marketing of stuff people might buy for pets? Maybe training or pet health advice you've collected from experts selling at a low cost? Just brainstorming here.
I started a coding youtube channel that used to make around $1000/mo before the algorithm changes started favoring channels that uploaded more often and my ad rates dropped from about $20CPM to around $4CPM: http://www.youtube.com/devfactor

Now it makes around $100/mo

When I was working on it it was around 4h of work to create a 10min video tutorial. I think I have around 100 tutorials.

When I was making low income working for a startup I also did consulting on the side, charged 3-5k for small business websites. Now I work at a big company which pays me enough to survive high CoL so I don't do that anymore.

I've got two cash flow positive side-projects while maintaining full-time employment, having a life, wife, and kid.

BreezyPDF - https://breezypdf.com - Dead simple PDF generation from URLs. Comes with a rails middleware so all you have to do is add .pdf to the end of a URL to download a PDF of that URL.

HOALife - https://hoalife.com - A CC&R Inspection and Enforcement tool for property managers.

Was it difficult to get the early users? What did you do to get them to use your websites?
The first users were insanely hard to get. Getting new users never gets easy, but less-hard as you go.

First users were usually contacts that I had made within the spaces prior to building. Then old-fashioned marketing and sales pipelines.

I love how one of the Breezy testimonials is from HOALife. Way to dog-food!
Ha, I should probably update those to customers that are less biased
You are not the first, you won't be the last :-)
Don't worry OP, your secret is safe with us
I'm impressed at the HOALife being a side project. I've worked at companies doing something similar (different country) and it's a full time job maintaining and adding features to apps like that. If you are doing all the coding, marketing, web design, payment processing and support (and in my experience people want stuff fixed quick because they have inspections to do or they get kinda angry) in your spare time I really don't know how you do it, unless you are teaming up, employing people or just ridiculously efficient.
I do all the coding design and support, and some marketing and sales. I have a co-founder for HOALife that does a lot of the day-to-day work (his side-gig too)!
whoa. huge props for HOALife. any interest in selling? I'm interested in acquiring =) we're a growing player in the property services niche looking at different entry points into hoa's
Damn, I spent all night last night trying to get jspdf to work for me and gave up. Breezy looks like exactly what I needed! Serendipity.
Spent the better part of two years building a local food and drink promotion side gig. Building connections, making money, social life, growing photography skills and traveling for something I'm already doing in my life, eating and drinking. Cliche as it may be, that's the key, particularly when adding ANOTHER job on top of your day job. You have to enjoy the shit out of it.
Might not be your typical answer, but I launched an ecommerce store that’s been profitable since the first month. At first I targeted solo devs without much digital design skills, but it turns out that blank sketchpads are very useful to designers and design agencies as well. It’s done well enough where I continue to run out of each batch of inventory and it’s turned a small profit as I continue to order large and larger batches of product.

https://sketchpads.co

I love these. You should make whiteboard magnets!
That’s an interesting idea! I’ll look in to that
Wow, this is brilliant. So simple yet so useful. How do you plan to deal with competition? It seems like barriers to entry are low.
Linea App for iOS does this. If you have an iPad with an Apple Pencil it's awesome.
These are awesome. I’m a proposal manager, and I sketch out storyboards with pen and paper during the planning stage. Something like this with pages divided into 1/4ths and 1/8ths would be very helpful.
Brilliant. Best of luck to you.
Have you thought of making browser sketchpads with the orientation flipped so it's closer to the horizontal rectangles of most computer monitors?
I built my startup while keeping my job until it was impossible to sustain. I tried really hard to make it work as long as possible.

At the time I quit my job the startup was profitable and growing really fast. A few months later we started negotiating an acquisition and closed the deal after working less than a year on it full-time.

I work full time and get/test/ship washer/dryer/dishwasher spare parts in my, uh, spare time. It's profitable at 2000 pounds/month, and can go much, much higher. Fuck this shit because no one should just work 6-8 24/7.
You buy and sell spare parts?
I built Artpip (https://artpip.com) whilst working fulltime. Spent the odd weeknight and some weekends developing it over the course of a few months, then the same again when I added the pro mode once I realised it could actually make me some money.

Not sure you could classify it as a startup, but it makes me a few hundred dollars per month. I'd actually love to grow it more but I'm not sure what the best direction to take it in is. If anybody has any feedback or feels like getting involved, feel free to drop me a mail at "tom @ artpip.com"!

How about galleries of NASA pics, national parks, and other themes besides art?
That's cool! Where do your source your images from?
All from Wikipedia/Wikidata. Now they're served from my own database.
Side projects are healthy just keep adding features here and there you’ll be surprised at what users gravitate towards ;)
Nice!

How is the legal situation with these paintings? They are from well known artists (van Gogh, Monet, ...) - is it now possible to sell them because the artists are dead for a long time - I thought that maybe some descendants hold the (exclusive) right to sell them, but I may be wrong ...

Good luck with your endeavor.

That's what I do currently, I'm a full time product manager in a normal company, and I'm also working as a CTO at a startup, we are 3. Two people are working full time, and I only work part time (about 30h per week). I do that, because I like doing multilple things at the same time. But I think it is a very difficult life.

I can do that because I have no social life and everything is optimized so that I can work all the time. But I don't think I would recommend that to everyone.

Benefits are :

* You are never bored

* If one of your job annoys you, you can always balance with the other one

* You have a lot of money, because you have two salaries, but you also don't have the time to buy anything

* And you dont waste time on useless things

Disadvantages:

* No social life

* No time with familly

* No leisures

* Very tired all the time

Honestly having a startup is usually not only something you can focus on only the night, you need to answer clients during the day, you need to monitor everything all the time. But if you love working, this is definitely something that you can enjoy

How long have you been doing this for? Do you think this can be maintained over a long period of time?
I have been doing that since may last year, but at beginning I was working much less, maybe max 55h per week.

I have been doing 70h+ per week for 4 weeks now, and I don't think I can do much more, you really feel that working ask a lot of energy.

But to be honest, 55-60h is possible to maintain a very long period of time, since the 26 of september last year, I worked 2682 hours, which is in average 7,34 hours per day, 51,4 hours per week, and I'm not dead (yet)

Yes. if you have a balanced, reasonably healthy life style it is absolutely doable. I am able to handle it in my early 30s. In my 20s with all the partying going on it was sometimes a problem to stay focused 12+ hours on a single day book-ended by good rest.
"Very tired all the time" - Where I come from (EU) this is the reason why it's not allowed to work two jobs (>40h) if the employer doesn't approve.
I'm from France, it is not allowed to work more than 44h per week for a period of 12 weeks. But honestly it is difficult to set the same bar for everyone
It’s not just a question of fatigue but also that for intellectually innovative work, it’s rare to get more out of 40+ hour weeks than 20-30.

At least this is the case with kids.

In the US, often employment agreements come with clauses that prevent working other jobs, and sometimes even preventing any out-of-work activities that negatively affect job performance.
When you ask your employer for permission for a second job (insofar as that is strictly legal), it's usually not a given that they ask for an estimate of the hours per week you will put in it. Instead they will ask you about the work to see if it might infringe on their business. It's a measure made to ensure that you don't get into their water, not one to protect you. That is why it's in your work contract and not part of the actual law.
I'm in the UK and have never heard of this 'rule'?
Does you diet suffer? Exercise? Do you get to shower? Sleep much?
I used to exercise every day, now only 3 times a week but sports is more often a good way to gain more energy.

I sleep a lot, average 8h30 per day, I really need to sleep a lot

Sleep is good for the soul and mind! I don't know how people can go for extended times without sleep and still be productive...
i found the keto diet to be very complimentary to the founder lifestyle. you end up intermittently fasting because of work which helps boost all of the benefits of keto.
I, along with two other co-founders, have bootstrapped a profitable SaaS startup over the last two years while we all three maintained our day jobs. We all have families but have put in nights/weekends to get it where it is. I just made the jump and quit my day job and the other two are just about to do the same.

In retrospect, it was a much safer way to start a business because it took much of the uncertainty out of the equation and eliminated the financial stress. It was possible for us because our startup is a SaaS business, not all businesses can be bootstrapped or built with only nights and weekend efforts. I often wished it would go faster and still think we could have been profitable a year earlier than we were but with time being our biggest constraint it didn't happen. That was the tradeoff we made for financial stability. You have to be OK with small successes and slow progress that evolves into a business/product over time rather than one massive sprint to get an MVP ready to ship in a couple weeks/months.

Echoing what many have mentioned in this thread. Read your employment agreement for mentions of Intellectual Property, inventors clause, etc. I work full-time and I am launching a side business, but I have a licensing agreement in place with my employer that clearly states my ownership of my businesses IP in exchange for a free license of the product. There is a lot of grey area in employment agreements. Even if there isn't anything that is clearly stated (from your understanding) that would cause issues, it is up to debate in the court of law. The best plan of action is to speak with a lawyer. It took me six months and multiple revisions to my licensing agreement before it was signed, but I can now sleep better at night and launch my business!
I built bonsai.io/websolr.com while working at Twitter in 2010. I left in 2012, keeping a promise to a co-founder that I'd leave if we hit $1M ARR.

There were definitely a couple months of pager/ops overload where I hit 100hr workweeks and multiple hundreds of pagers per week. Hypervisor bugs meant that some tasks were hard to automate, and that automation would stochastically fail, so I stayed up til 4am watching the logs and correcting issues, then went back into the office at 10am.

Basically, it was a reasonable hedging strategy against either company's failure, but given both succeeded, I lost a good chunk of what I would have made if I was "all in" on either. Plus, it was about as miserable as it sounds, though I learned a ton.

Any insightful takeaways from "watching the logs" and "correcting issues" in terms of what you would do differently?
If you aren't automatically rolling instances frequently, you will inevitably have some machines that were theoretically cattle but in practice are pets. (This is much easier today with k8s/mesos)

More generally, when you claim in system design that you have invariants, if you aren't using automation to enforce your invariants, they will inevitably be bypassed to your detriment by eager and/or lazy engineers. You will find this out at the worst possible time.

We had a different turn of events in our case. Me and my co-founder we were working on the startup, while on our full-time jobs, and we got some grants from governments to allow us to quit and persuit it full time. This was 4 years ago and we are still going strong with sales and grants. Never underestimate the opportunities for free money! Governments, councils, schemes, all have projections, agentas and budgets and if your startup aligns with them you can get 10k to 150k usd just by writing a few proposals..
Any good resources for which grants are available for tech?
Can you post some sources to this information?
Dont have any guide tbh, it is all luck and prercistence. Just to give you an idea, we apply to multiple grants every 1-2 weeks from websites like younoodle, f6s and we keep an spreadsheet with all the deadlines of each grant (that might have their own website). All this while doing a hardware product and running the baby/startup.

Talking with people, the first barrier we see is that people think they can't get or don't deserve grants. They give excuses like, "Oh I never been to country X", "I'm not a resident there", "It's just an idea", etc etc.

Most grants will ask you to go to country X, incorporate there in some cases (to attract talent), or get involved and help the ecosystem of that region. For others you just submit a proposal with milestones and you have check, presentations and writeups (and ultimately you do the things you promised).

Some examples of grants are, startupInsertXCountry (e.g. StartupChile, StartupPeru, Startup Puerto Rico - P18), LaunchKC (Kansas City), EU H2020 (hard) but also H2020 sub-programs that got H2020 funding for a cause and pass it on to startups as a challenge (robotics challenges, Big-data challenges), HotDesQ (AUS), and many many many more countries that want to be like Silicon Valey)

Hope this helps!