Security Deposit Interest Calculator
Introduction: why security deposit interest matters for tenants and landlords
A security deposit can sit with a landlord for months or years, and the interest earned on that money is often part of the final refund or annual accounting. This calculator turns the deposit amount, the interest rate, the compounding method, and the lease dates into a clear estimate so tenants and landlords can see what should have accrued.
It is most helpful when the numbers match the way the deposit is actually handled in the lease or by local law. The notes on this page explain the fields, date handling, and interest method so the estimate is easier to compare with a statement, a move-out settlement, or your own records. When two people apply different rules to the same deposit, the result can look inconsistent even when the arithmetic is correct.
The sections below show how security deposit interest is calculated, how to enter the dates and rate, how to read the result, and which assumptions matter most before you rely on the estimate.
Why calculate security deposit interest?
The practical question behind a security deposit interest calculation is whether the landlord owes interest on the money held during the tenancy, and if so, how much. In real life, that usually means comparing a lease clause, a statutory rate, or an annual statement against your own figures. The calculator gives you a consistent way to estimate the amount so you can check the refund or payment with confidence.
Before you begin, state the deposit question in plain language. For example: Is interest paid yearly or at move-out, does the rate change each year, should the deposit be compounded, or is simple interest the correct method? Once the question is clear, it is much easier to tell whether the form fields match the rule you are trying to verify.
How to use this security deposit interest calculator
- Enter amount with the unit shown beside the field.
- Enter rate with the unit shown beside the field.
- Enter interest-type with the unit shown beside the field.
- Enter start with the unit shown beside the field.
- Enter end with the unit shown beside the field.
- Run the calculation again to update the security deposit interest results panel.
- Review the output’s unit, rough size, and direction before comparing lease scenarios.
If you are comparing lease terms or annual statements, keep a note of the deposit amount, rate, and date range so you can reproduce the security deposit interest figure later.
Inputs for security deposit interest: how to pick good values
The form collects the numbers that determine how much interest has accrued on a rental deposit. Common mistakes come from entering the wrong deposit amount, using a rate from the wrong year, or picking a compounding method that does not match the lease or local statute. Use the checklist below as you fill in the fields:
- Units: confirm the label next to each field and keep the entry consistent with the lease or statement you are checking.
- Ranges: if your state or city sets limits, treat the displayed bounds as the calculator’s safe range for deposit interest.
- Defaults: any prefilled values are only placeholders; replace them with your own deposit and rate before trusting the output.
- Consistency: if the lease says the deposit compounds annually but the form is set to monthly, the result will drift from the official figure.
Common inputs for tools like Security Deposit Interest Calculator include:
- amount: the original security deposit collected when the lease began.
- rate: the annual percentage used to calculate the deposit’s growth over time.
- interest-type: the calculation method that matches the lease clause or local tenant rule.
- start: the date the landlord began holding the deposit or the date interest started to accrue.
- end: the date through which you want to estimate the accrued deposit interest.
If you are unsure about a rate or end date, run one scenario with the conservative interpretation and another with the more generous one. That gives you a realistic range for the deposit interest instead of a single number you may need to correct later.
Security deposit interest formulas: how the calculator turns inputs into results
Every method here starts from the same three ingredients: the deposit principal P, the annual rate r written as a decimal (2% becomes 0.02), and the holding time t in years. The calculator finds t by counting the exact days between your start and end dates and dividing by 365, so a 182-day tenancy is treated as about 0.499 years rather than being rounded to a whole year.
Simple interest — the method most tenant statutes require — applies the rate once to the original deposit and prorates it by time:
Annual compounding lets each year's interest earn interest of its own, so the accrued amount is the compounded balance minus the original principal:
Monthly compounding divides the annual rate into twelve monthly steps and compounds over the number of months held:
In all three, I is the interest owed; the total the landlord should return is the principal plus that interest, P + I. At the small rates common to deposit accounts the three formulas land close together for a single year, but the compounding versions pull ahead as a tenancy stretches across several renewals. If a longer holding period does not raise the interest the way you expect, recheck the rate, the two dates, and the interest type before questioning the arithmetic.
Worked example: $1,500 security deposit at 1% over two years (step-by-step)
Say a landlord held a $1,500 deposit at a 1% annual rate across a two-year lease, with a start date of Jan 1, 2024 and an end date of Jan 1, 2026. That span is 731 days, which the calculator divides by 365 to get about 2.003 years — near enough to treat as two years for a hand check.
- Simple interest: 1,500 × 0.01 × 2 = $30.00. The refund should be $1,530.00.
- Compounded annually: 1,500 × [(1.01)2 − 1] = 1,500 × 0.0201 = $30.15, so $1,530.15.
- Compounded monthly: 1,500 × [(1 + 0.01/12)24 − 1] ≈ 1,500 × 0.02019 = $30.29, so $1,530.29.
What the calculator returns, and why it differs. Those three lines assume exactly two years. The span from 1 January 2024 to 1 January 2026 is 731 days, because 2024 is a leap year, and on a 365-day basis that is 2.00274 years rather than 2. The calculator prorates by the actual days held, so it reports $30.04, $30.19 and $30.33 respectively. Switching the day-count basis to actual days in each calendar year returns exactly 2.00000 years and reproduces the textbook $30.00. That gap of a few cents is the whole reason the basis selector exists: statutes differ on which convention applies, and on a large deposit over a long tenancy the choice is worth real money.
The three methods differ by only about 29 cents on this deposit — a reminder that at deposit-account rates the compounding choice barely moves the number over two years, though the gap widens on larger deposits or longer tenancies. After you click Calculate, match the results panel against your lease period and statement. If the figure looks far off, check whether you entered a monthly rate where a yearly one belongs, or reversed the two dates. If it looks right, change one input at a time — amount, rate, or method — and watch how the accrued interest responds.
Comparison table: how the deposit amount drives the interest owed
The table below varies only the deposit amount while holding the rate at 1%, simple interest, over a two-year lease. Because simple interest is linear in the principal, the interest scales in exact proportion — a useful reality check when you compare a landlord's figure against your own.
| Scenario | Deposit | Rate & term | Interest owed | What it tells you |
|---|---|---|---|---|
| Conservative (−20%) | $1,200 | 1% simple, 2 yr | $24.00 | A smaller deposit earns proportionally less; the $6 drop mirrors the 20% cut. |
| Baseline | $1,500 | 1% simple, 2 yr | $30.00 | The reference case a one-month-rent deposit might produce. |
| Aggressive (+20%) | $1,800 | 1% simple, 2 yr | $36.00 | A larger deposit earns proportionally more; $6 above baseline, matching the 20% rise. |
Run the same three deposits in the live calculator to confirm the pattern, then swap in a higher rate to see how much faster the interest grows when the statutory rate — not just the principal — climbs.
How to interpret the security deposit interest result
The results panel is meant to summarize the interest owed on the rental deposit, not to show every intermediate step. When the figure appears, ask three questions: does the unit match the way your lease or statute states interest, is the amount plausible for the deposit and date range, and does the result move in the expected direction if you change the amount, rate, or compounding method? If all three checks pass, the estimate is probably usable.
When available, the Copy Result button gives you a record of the scenario you just ran. Saving that text is handy if you want to compare a landlord’s statement with your own estimate, show a roommate the numbers, or keep documentation for a deposit dispute. It also lets you reproduce the calculation later without re-entering the same dates.
Choosing a day-count basis and reading the accrual curve
Interest on a deposit is almost never a whole number of years, so every calculation has to convert a span of days into a fraction of a year, and the convention used changes the answer. The three offered here are the ones that appear in leases and statutes. A 365-day year is the common default. A 360-day banker's year, inherited from bond markets, makes each day worth marginally more. The actual-days option divides each calendar year by its own length, so a leap year counts 366 days, and it is the only basis under which an anniversary-to-anniversary hold returns exactly one year.
The chart draws all three accrual methods together over the period held, with the one you selected drawn heavily. Over a short tenancy at typical deposit rates the three curves are almost indistinguishable, which is the honest visual answer to whether compounding matters here. Stretch the term or raise the rate and they separate visibly. The results table reports what the other two methods would have produced alongside your own, so the choice is never hidden inside the number.
One further output is worth attention: the effective annual yield actually paid, computed as . For simple interest over more than a year this comes out slightly below the stated rate, which is not an error: simple interest does not pay interest on interest, so its effective yield falls short of a nominally identical compounding rate.
Sources. The arithmetic is standard; whether interest is owed at all is a matter of state and local law, which these point to rather than summarise.
- Tenant rights by state, including where to find security-deposit rules and any interest requirement: US Department of Housing and Urban Development, Tenant Rights, Laws and Protections by state.
- What to do when a deposit is not returned, and how to document a dispute: USA.gov, Rental housing help and tenant complaints.
- Simple against compound interest and the effective annual yield relationship: US Securities and Exchange Commission, Investor.gov, compound interest.
- Free legal help directories for tenants who cannot afford a lawyer: Legal Services Corporation, Get Legal Help.
Questions about security deposit interest
Am I actually owed interest on my security deposit?
It depends entirely on where the property is. Some states and cities require landlords to hold deposits in an interest-bearing account and pay the interest to the tenant, sometimes annually and sometimes at the end of the tenancy, occasionally at a rate set each year by a housing authority. Many other jurisdictions require nothing at all. This calculator does the arithmetic once you know the rule; it cannot tell you what the rule is where you live.
Which day-count basis should I use?
Use whichever the governing statute or lease specifies, and if neither says, the 365-day year is the usual default. A 360-day banker's year makes each day worth slightly more and so pays marginally more interest for the same period. The actual-days option divides each calendar year by its own length, so a leap year counts 366 days, which is the only basis that returns exactly one year for a genuine anniversary-to-anniversary hold.
Why does the calculator disagree with my hand calculation by a few cents?
Almost always because you used whole years and it used actual days. A lease running from 1 January 2024 to 1 January 2026 spans 731 days rather than 730, since 2024 is a leap year, and 731 divided by 365 is 2.00274 years. That extra fraction is worth about four cents on a 1,500 dollar deposit at one percent. The results table shows the exact year figure it used so the difference can always be traced.
Should the interest be simple or compounded?
Most tenant statutes that require interest specify simple interest, which is why it is the default here. Compounding appears when the deposit genuinely sits in an interest-bearing account whose own terms compound, or when a lease says so. At deposit-account rates the difference is small over a short tenancy, but it grows with both the rate and the term, and the results table now reports what the other two methods would have produced so the gap is never hidden.
Can the landlord keep the interest?
In some jurisdictions yes, in others no, and in a few the landlord may retain a stated administrative percentage and must pass on the rest. Where interest is owed, failing to pay it can carry penalties well beyond the interest itself. Because the amounts are usually small relative to the deposit, the more common dispute is about deductions from the principal rather than the interest on it.
Does this account for deductions taken from the deposit?
No. It assumes the full principal was held for the whole period. If a landlord lawfully deducted for damage, interest is normally still calculated on the amount actually held over the time it was held, so a mid-tenancy deduction would require splitting the calculation into two periods and running each separately. Keep the itemised deduction statement, since that is what any dispute will turn on.
Limitations and assumptions for security deposit interest
No deposit-interest calculator can capture every lease clause, local statute, or payment schedule. This tool is designed to provide a practical estimate of what interest might be owed on a security deposit, not a legal ruling. Keep these common limitations in mind:
- Input interpretation: the label matters; a deposit, a rate, and a compounding choice are not interchangeable.
- Unit conversions: convert percentages and dates carefully before entering values.
- Linearity: some jurisdictions allow simple interest only, while others treat annual and monthly compounding differently.
- Rounding: shown amounts may be rounded to the nearest cent, so tiny differences from a lease statement are normal.
- Missing factors: local notice rules, penalties, or withheld charges may not be included.
If you rely on the output for a legal dispute or final refund check, treat it as a planning estimate and confirm the controlling tenant-law rules for your city or state. A calculator is most valuable when it makes the lease assumptions explicit, because that gives you a clear trail for checking the interest figure against official guidance.
Mini-game: Escrow Jar
Interest drips into your deposit one coin at a time — but so do the landlord's deductions. Slide the escrow jar under the falling gold coins to bank accrued interest, and dodge the red deduction tags for damage and cleaning charges. Catch three deductions and the lease ends early. See how much interest you can secure before the tenancy runs out.