Q: The unit is subject to statewide rent control (no local ordinance). I didn't know what the percentage was on how much I could raise the rent, so I overcharged the tenant more than what was allowed. She didn't complain about the illegal rent increase and we get along well. What should I do?
A: Even though the tenant has acquiesced to the rent increase and you have an amicable rental relationship now, your error is a ticking time bomb.
It is prudent to correct your mistake by refunding the rent money you overcharged her and setting the record straight on what the actual rent is. For example, if the rent increase is $30 above what you could legally charge and the tenant has been in possession of the unit for 7 months. You would be advised to give her back $210.
If you allow the illegal rent increase to continue and there is some sort of dispute in the rental relationship and you get sued, you can rack up thousands of dollars in rent that has to be disgorged if you let too much time pass. Better to fix the illegal rent increase early on and not let the issue fester.
There is a law being drafted that would make statewide rent increases (pegged on local changes in inflation) more transparent for housing providers, but in the meantime, the California Apartment Association has a nifty tool to get the accurate number by entering your particular area.