Legal Question in Landlord & Tenant Law in California

That depends on the terms of your lease or rental agreement. It should say. My leases say the deposit is for a deposit, not last month's rent, unless the tenant requests a walk-through before the last month's rent is due and it looks like there will be enough to cover any repairs/cleaning, and the last month's rent. If a tenant just takes off without paying the last month's rent, I take it out of the deposit, but I also report them to credit bureaus as defaulting on their lease because that is what it is.