Security Deposit and Deposit Interest Calculator by State

How to use the security deposit calculator

Enter four things:

• Monthly rent. Most caps are set as a multiple of it.
• State.
• Deposit you plan to collect or already hold.
• Months held, so the tool can estimate interest where your state requires it.

The calculator returns the maximum deposit allowed, a note on interest (whether it’s owed, at what rate, and roughly how much), and the deadline for returning the deposit after the tenant moves out.

How the calculation works

• Maximum deposit = monthly rent x your state’s multiple (or “no statutory limit”)
• Interest, where a simple rate applies = interest-bearing amount x annual rate x (months held / 12)
• Return deadline = your state’s day count, from the date set in its statute (often move-out or surrender of possession)

Interest rules vary more than anything else. Some states set a flat rate, some tie it to a bank or Treasury rate, and some only count part of the deposit.

Worked examples

Ohio. Rent is $1,400 and you hold a $2,100 deposit for 12 months. Ohio has no deposit cap, but under Ohio Rev. Code § 5321.16 you owe 5% a year on the part above the greater of $50 or one month’s rent, if the tenant stays at least six months.

• Interest-bearing part: $2,100 - $1,400 = $700
• Interest for one year: $700 x 5% = $35
• Return deadline: 30 days

Charge a deposit of $1,400 instead and you owe no interest at all.

Massachusetts. Rent is $2,000. Under Mass. Gen. Laws ch. 186, § 15B, the most you can take is one month’s rent, $2,000, though you may also collect first and last month’s rent and a lock-change fee. The deposit must sit in a separate interest-bearing account in a Massachusetts bank, and you owe 5% a year or the bank’s actual rate if lower, paid annually. At 5%, a year’s interest is $100. The return deadline is 30 days. The paperwork is strict: a receipt with the bank details within 30 days and a signed statement of condition within 10 days. Violations can mean treble damages.

California. Rent is $2,500. For deposits collected on or after July 1, 2024, the cap is one month’s rent, $2,500 (Cal. Civ. Code § 1950.5). A natural person or family LLC or trust owning no more than two residential rental properties with no more than four units total may charge up to two months. There’s no statewide interest rule, but San Francisco, Berkeley and Santa Monica require it. You have 21 days to return the deposit with an itemized statement.

What a good result looks like

The right deposit is usually at or below your state’s cap and high enough to cover a month of unpaid rent plus typical damage. Charging the maximum isn’t always smart. In Ohio, anything above one month’s rent creates an interest obligation. In a slow market, a lower deposit can fill a unit faster.

Put a reminder on your calendar for the return deadline the day the tenant gives notice, so the itemized list goes out on time.

Limits of this calculator

• City rules. Chicago, San Francisco and other cities set their own interest rates and penalties, and Cook County caps suburban deposits at 1.5 months.
• Variable rates. Where the rate changes each year (Connecticut’s is set annually by the Banking Commissioner; Maryland’s tracks a Treasury rate with a 1.5% floor) or depends on what the bank pays (New Jersey, North Dakota), the tool gives a note rather than an exact figure. Minnesota is simpler: 1% simple interest a year.
• Exceptions. Pet deposits, furnished units, tenants 62 or older in Connecticut, and lease length can change the cap.
• General information, not legal advice. When a deduction is disputed, talk to a local attorney.