There are no state laws in California that address overcharging a subtenant or roommate. That said, certain cities—including San Francisco and Berkeley—have their own local laws protecting subletters from potential price-gouging.
San Francisco is quite strict about how much you can ask subletters to pay in rent. If you decide to move out and sublet your entire unit, then you can't charge your subletter any more rent than you're actually paying to the owner of the property.1
If, on the other hand, you sublet just a part of your unit (one bedroom, for example), you can't charge your subtenant any more than their proportional share of the total rent.2
Berkeley also limits how much you can legally charge a subletter. A master tenant (that's you!) subletting the entire unit can't charge a subtenant more than they pay in rent to the landlord or property manager.
If a master tenant brings in a subletter as a roommate, they can't charge more than an amount that's "substantially proportional" to the space occupied by the subtenant.3 You could try dividing your total rent by the square footage of the apartment, then multiplying that number by the square footage of the room you're subletting (plus, it's probably fair to add an additional amount if the bedroom has way better light or a private bathroom or any other major perks).
The information provided on this website does not, and is not intended to, constitute legal advice.