Security deposit interest calculator

Interest on the balance actually held, for the days it was actually held — through top-ups, part-years, and anything already paid out. Prints a statement showing every period.

The deposit

The amount and the date it was paid. Add a second line if the deposit was topped up later — interest runs on each balance for the time it was actually held, which is the part that gets lost when this is done by hand.

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The rate
We haven’t verified any state’s statutory interest rate.

So this asks you rather than guessing. The rate is usually in your lease, in your state’s security-deposit statute, or on the statement from the account the deposit sits in. Some states set it annually, which is why a number copied off a blog last year is worth re-checking.

If the statute says simple or noncompounded, take the first. Where a statute is silent, simple is the conservative reading and the one easier to defend.

Interest already paid

Only if some has already been handed over or credited against rent — several states require that every year. Leave this empty if none has.

The tenancy

The move-out date, or today if the tenancy is still running and you want the position to date.

Why this isn’t one multiplication

The easy version is deposit × rate × whole years, and it is wrong in three ordinary situations. A tenancy almost never ends on an anniversary, so the last period is a part-year. A deposit that was topped up when the rent went up earns on two different balances over two different stretches. And where interest has been paid or credited along the way — which several states require every year — only the remainder is owed at the end.

Each of those splits the term into periods, and the easy version collapses them. Notably, it collapses them in the landlord’s favour every time: whole years rounds the term down, and a single balance is almost always the smaller one. That is the arithmetic this does properly, and prints, so the number can be checked rather than trusted.

What we can’t tell you

Your rate. We have not verified a single state’s statutory interest rule against its statute — not one of the fifty — so this tool asks you for the rate instead of filling one in. That is a deliberate gap, not an oversight. Several states set the rate annually through a banking regulator, a figure copied from an article last year is often already stale, and a confidently wrong rate on a document somebody hands their landlord is worse than no tool at all.

Where to find it: your lease, your state’s security-deposit statute, the statement from the account the deposit sits in, or a local tenant advice service. If you have the rate, everything after it is arithmetic, and the arithmetic is here.

How the days are counted

Actual days over a 365-day year — the convention easiest to check by hand and the one a tenant service or a small-claims court will recognise. Leap days count as days, so a term spanning one earns 366/365 of the annual rate. There are four defensible day-count conventions and they give slightly different answers; saying which one is in use beats picking one quietly.

The rest of the deposit

Interest is usually the last question about a deposit rather than the first. If what you actually need is whether deductions were fair, the deduction calculator prorates charges by an item’s remaining useful life instead of billing a whole carpet. Landlords returning a deposit want the deposit return letter, which itemizes against your state’s deadline. Tenants who never got one want the demand letter, which works out whether the landlord is late and by how many days.

General information, not legal advice. CompliMaint is not a law firm, has not verified any state’s deposit-interest requirement, and takes no view on whether interest is owed in your situation. The rate is whatever you enter; the arithmetic against it is ours. Everything runs on your device.