Legal Question in Real Estate Law in California

Re: Late fees- are they legal?

California does not have a fixed statutory maximum late fee. The maximum late fee is set by the court's view as to what is reasonable and unreasonable. Charges of more than 10% for being one day late are more likely than not unreasonable and therefore unlawful.

The landlord has a better chance if the late-fee provision is written into the lease, but this doesn't mean he can't charge a late fee if the lease is silent on the matter, nor does it mean that a late fee is reasonable (and thus lawful) just because it's in the lease the tenant signed.