There is no single national limit
Unlike some consumer protections, there is no federal cap on security deposits — the limit, if there is one, comes from your state (and sometimes your city). That means the honest answer to "how much can my landlord charge" is "check your state," not a single number that applies everywhere. Some states cap deposits at a set number of months' rent, some set no dollar limit at all, and a few have different rules depending on whether the unit is furnished. See the state-by-state security deposit rules or run the numbers with the security deposit calculator for what applies to you.
This is one of the questions where a generic answer can actually cost you money — a number that is correct for one state can be flatly wrong, or half the real figure, for another. If you are budgeting for a move, treat the deposit as a genuine unknown until you look up your specific state, rather than assuming "first month, last month, and a deposit equal to one month's rent" the way it works in some places.
A verified example: California
California's cap is a useful, verified illustration of how these laws work. As of July 1, 2024, a landlord generally cannot demand more than one month's rent as a security deposit. There is a narrow exception: a landlord who is a natural person (or an LLC made up entirely of natural persons) and who owns no more than two rental properties totaling four units or fewer can charge up to two months' rent — but that exception does not apply if the prospective tenant is a service member (Cal. Civ. Code § 1950.5). That is one real state's rule, in detail — it tells you nothing about what your own state allows unless you actually live in California.
Why "no limit" states still have rules
Some states set no maximum dollar amount at all, which surprises a lot of renters. That does not mean anything goes — those states still require the deposit to be returned within a deadline, itemized if any of it is withheld, and never kept for anything beyond legitimate damage, unpaid rent, or necessary cleaning. A high or uncapped deposit is a bigger check to write up front, but it does not change what the landlord can actually deduct at move-out.
Deposits labeled "nonrefundable"
Watch for any deposit or fee your lease calls "nonrefundable." Some states do not allow a security deposit to be labeled that way at all — California's statute says outright that "a lease or rental agreement shall not contain a provision characterizing any security as 'nonrefundable'" (Cal. Civ. Code § 1950.5). Whether that specific rule applies to you depends on your state, but it is worth checking any nonrefundable label against your own state's law rather than assuming it is enforceable just because it is in writing.
Pet deposits and furnished units
Some states treat a pet deposit as a separate charge on top of the security deposit cap; others count it toward the same overall limit no matter what it is called. California is an example of the second approach — its statute defines "security" broadly enough that a fee labeled as a pet deposit still counts toward the same one- or two-month cap. Furnished units can also be treated differently from unfurnished ones for deposit purposes, depending on your state and your lease. None of this is consistent nationwide, so check your specific state rather than assuming either pattern applies to you.
Reading your lease's fee list closely
Before you assume a charge is a separate, additional fee, check whether your lease (or your state's law) actually treats it that way. A landlord might call something a "pet fee," a "key deposit," or a "move-in fee," but depending on where you live, some of those labels are just security by another name, and they may need to be counted toward the same overall cap. This is exactly the kind of detail that is easy to miss when you are looking at a total dollar figure rather than reading the fee breakdown line by line.
What to do if you were overcharged
If your landlord charged more than your state allows, the excess may not be enforceable, and some states add a penalty on top. Document exactly what you paid and when, and check your state's actual limit before you raise it — the security deposit calculator walks through the math for your state and rent amount. Upload your lease to Honestkey to see whether your deposit and any related fees add up to more than your state allows.