If you are a real engineer you would already know the answer because there's a defined path. If you are a software developer/programmer that's not engineering, so you can call yourself that whenever you want, it's meaningless. You can also call yourself a ninja or rockstar.
I assume this is for a role where you can get an engineering license. I would say after passing the requirements in your country that enables you obtain the license, then you can call yourself an engineer.
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[ 3.0 ms ] story [ 27.9 ms ] threaddegree < 2 years experience: training/require supervision
degree 2 < 5 years: experienced, capable, get responsibility
degree > 5 years: lead positions/expert (if narrow focus)
so i would say degree + 2 years you can say 'engineer' (without training wheels)
https://www.theatlantic.com/technology/archive/2015/11/progr...