Simple Interest Calculator
Solve for interest, principal, rate or time — in years, months or days.
Calculated locally in your browser. Nothing you enter is uploaded or stored.
- Free — no signup, no account, no watermark
- Runs entirely in your browser — nothing is uploaded to a server
- Works on mobile, tablet and desktop
- Instant — results appear as soon as you enter your input
Why this is private
- Calculated locally in your browser. Nothing you enter is uploaded or stored.
- Open your browser's DevTools → Network tab while using this tool — you won't see a request carrying your input, because it never leaves your device.
- Nothing you enter is uploaded to a server or shared with us — the processing happens entirely on your device.
Overview
Calculates simple interest, where interest accrues only on the original principal — not on previously earned interest. Solve for interest, principal, rate or time — whichever one you don't already know — and enter the time period in years, months or days (360- or 365-day year).
How to use it
- 1Choose which value to solve for: interest, principal, rate or time.
- 2Enter the other three — time accepts years, months or days.
- 3View the solved value and the full breakdown.
Formula
Simple interest
I = P × r × t / 100
P = principal, r = annual rate (%), t = years. Rearranged to solve for whichever variable is unknown.
Tips
- This calculator provides an estimate for planning purposes only and is not financial advice.
Frequently asked questions
What people use it for
Work out interest on a short-term loanMany personal and informal loans quote simple interest — check what you'll actually repay.
Find the deposit needed for a target returnSolve for principal: "I want ₹50,000 in interest after 3 years at 8% — how much do I need to deposit?"
Work out the rate you actually gotSolve for rate from a real payout: "I deposited ₹1,00,000 and received ₹15,000 interest over 2 years."
Calculate interest on a delayed payment for a number of daysApply a simple-interest rate to an overdue invoice for an exact day count, in either a 360- or 365-day year convention.
Check a fixed-return instrumentSome bonds and deposits pay simple interest on the face value.
Compare simple vs compoundRun the same inputs here and in the compound calculator to see the gap.
Related guides
- Reduce EMI or reduce tenure after a part payment: which saves more?Both lower your total interest, but not by the same amount. Here's the trade-off, a worked example, and how to compare your own loan.
- How to calculate a home loan foreclosure amountOutstanding principal, accrued interest, charges and tax — what goes into a loan foreclosure (pre-closure) figure, and why the bank's number can differ.
- SIP vs. lumpsum: what the math actually saysSystematic investing and lump-sum investing solve different problems. Here's how to reason about which one fits your situation.
- How to calculate EMI (and why the formula looks so intimidating)A plain-English walkthrough of the EMI formula, what each variable means, and a worked example you can check by hand.
Related tools
All finance toolsCompound Interest CalculatorCalculate compound interest with configurable compounding frequency and optional regular contributions.Loan CalculatorCompare loan repayment options, and see how an extra payment speeds up payoff.EMI CalculatorCalculate your monthly EMI, full amortization schedule, and part-payment or foreclosure savings.SIP CalculatorProject the future value of monthly SIP investments, or compare against a lumpsum.
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Simple Interest Calculator