Ask HN: How to account for annual prepayments in SaaS startups MRR?

Imagine we have $10,000 MRR. Now, we close a customer worth $500/month, but he pays annually, so we granted him a 1 month discount ($500x11=$5,500). Do we now:

- add the discounted $5,500/12 = $458.33 to the MRR - add $550 to the MRR (because that's the plan the customer is on) - add $5500 to the current month's MRR - leave the MRR untouched

We used to go with the first solution (as it seems* the most "fiscally conservative"), but the problem is that we have a huge number of customers paying annually (roughly 80%), and our MRR does not account for that. So we report $10,000 MRR, but there will be only coming $2,000 actual bucks in the next month, because all the other customers are on annual plans (and that revenue may already be spent etc.). Makes calculating a burn rate and reporting to investors difficult. ("Why do you need $100,000 for a 6 month runway when you have $10,000 MRR?" - "Well, because we already got $80,000 in pre-payments and spent it.")

Is there another way to go or should I report a different metric?