Rex says
Money math without the spreadsheet headache. Plug in your numbers and I'll show you exactly where the dollars land.
Try a scenario
Click to load — tweak from there.Inputs
Result
Interest owed to tenant
$40.50
Total refund due (deposit + interest)
$1,840.50
Annualized interest amount
$27.00
Simple interest alternative
$40.50
Compound interest alternative
$40.93
Psst — share this and help Rex grow
One click, a permanent link with your numbers baked in.
How to use this
- 1Enter security deposit amount ($).
- 2Enter statutory annual interest rate (%).
- 3Enter months held.
- 4Enter interest method.
- 5Read your interest owed to tenant on the right — it updates as you type.
- 6Hit Share to keep the scenario or send it to someone.
About this calculator
A number of states and cities — including Illinois (Chicago and Cook County), Massachusetts, Connecticut, and New York City rent-stabilized units — require landlords to pay tenants interest on their security deposit, sometimes annually and sometimes only at move-out. Rates and rules vary widely: some jurisdictions use a fixed statutory rate, others peg it to the Federal Reserve discount rate or a bank passbook rate. This calculator applies a simple annual rate to the deposit over the holding period so you can estimate what's owed, but you must confirm your specific jurisdiction's rate and whether it compounds, since getting this wrong is a common source of security deposit lawsuits with automatic penalty damages attached.
Worked example
Using the values the calculator loads with:
Inputs
- Security deposit amount: 1800 $
- Statutory annual interest rate: 1.5 %
- Months held: 18
- Interest method: Simple interest
Results
- Interest owed to tenant: $40.50
- Total refund due (deposit + interest): $1,840.50
- Annualized interest amount: $27.00
- Simple interest alternative: $40.50
- Compound interest alternative: $40.93
What each field means
Inputs
- Security deposit amount ($)
- The security deposit amount used in the calculation, measured in $. Starts at 1800 $ so you have a working example on load.
- Statutory annual interest rate (%)
- The statutory annual interest rate used in the calculation, measured in %. Starts at 1.5 % so you have a working example on load. Accepted range: 0–10 %.
- Months held
- The months held used in the calculation. Starts at 18 so you have a working example on load. Accepted range: 0–240.
- Interest method
- Pick the option that matches your situation — the maths changes per option. Choices: Simple interest, Monthly compounding.
Results
- Interest owed to tenant
- Returned as a money amount in US dollars and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Total refund due (deposit + interest)
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Annualized interest amount
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Simple interest alternative
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Compound interest alternative
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
Which states require deposit interest?
Illinois (for buildings with 25+ units in certain municipalities), Massachusetts, Connecticut, New Jersey, Maryland, New York City, and a handful of other cities require it, often with different rates and payout schedules. Most states have no such requirement at all, so check your specific state and city before assuming this applies.
Is the rate fixed or does it change every year?
It depends on the jurisdiction. Connecticut ties its rate to the deposit guaranty fund rate and updates it annually; Illinois uses the Illinois Deposit rate published by the state comptroller. You need the current published rate for your holding period, not a single flat number, if the tenancy spans multiple years with rate changes.
What happens if a landlord fails to pay required interest?
Many jurisdictions impose penalties well beyond the interest owed — some allow the tenant to sue for two or three times the deposit amount, plus attorney's fees. This is one of the more litigated areas of landlord-tenant law precisely because the penalties are disproportionate to the small dollar amounts involved.
Do I pay interest annually or only at move-out?
Rules vary: some jurisdictions require annual payment or credit toward rent, others only require it be included in the final deposit return. Illinois requires annual payment for covered buildings; check your local ordinance rather than assuming a lump-sum-at-move-out approach is compliant.
Accuracy and limitations
- Results are estimates before tax, fees, and inflation unless an input explicitly covers them.
- Rates are treated as fixed for the whole period — variable-rate products will drift from this projection.
- This is educational maths, not financial advice. Check anything contractual with the lender or your accountant.
Related tools
Cite this calculator
Writing about this topic? Grab a citation — every link helps keep these tools free.
RevenueLab. (2026). Security Deposit Interest Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/security-deposit-interest
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/security-deposit-interest" target="_blank" rel="noopener">Security Deposit Interest Calculator — RevenueLab</a> (2026).</p>
Source: [Security Deposit Interest Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/security-deposit-interest) (2026).