Simple Interest

Interest and total repayment on a principal at a fixed rate.

How Simple Interest works

Calculate simple interest from principal, annual rate and time in years or months. Everything happens inside this page: the tool reads your input, runs the calculation or conversion locally, and hands the result back to you. Nothing is transmitted, because there is no backend to transmit it to.

That design choice is deliberate. Most free tool sites upload your files to a server, process them there, and quietly keep a copy. Toolcin cannot do that — the site is a set of static files. If your connection dropped the moment the page finished loading, every tool would still work.

The formula, and why it is smaller

Simple interest is I = P × R × T ÷ 100, where T is in years. On 100,000 at 8% for three years that is 24,000, and the total repayable is 124,000.

Interest is charged only on the original principal. It is never added back to earn interest of its own, which is exactly what compound interest does — and why the gap between the two grows with time rather than staying fixed.

Months and part-years

The tool accepts years or months; months are converted by dividing by 12, so 18 months is 1.5 years. That is simple-interest convention and matches how most short-term loans and informal arrangements are quoted.

What it does not do is day-count conventions — some instruments use actual/365, others 30/360, and the difference shows up in the last few rupees of a calculation. For anything with a legal agreement, use the convention named in the contract.

Principal	Rate	Time	Interest
100,000	8%	1 year	8,000
100,000	8%	3 years	24,000
100,000	8%	18 months	12,000
250,000	12%	2 years	60,000

Where simple interest is the right model

Most personal loans quoted as flat rate use it, which makes them look cheaper than they are — a flat 8% on a reducing balance is not the same as an 8% APR. Short-term lending, some car finance and informal arrangements all sit here.

If the interest is reinvested, use the compound interest page instead. Comparing the two side by side is the fastest way to see what compounding actually costs.

Good to know

Works offline once loaded, including on flights and in locked-down networks.
No file size limit beyond your device's own memory.
Free to use, with no account and no usage counter.
Results are produced locally, so they are not logged or shared with anyone.

Questions

How is it different from compound interest?

Simple interest is charged on the principal only, so it grows linearly.

Does it handle months?

Yes — switch the time unit to months and it converts to years.

Why is this different from my loan's interest?

A flat-rate loan uses simple interest on the original amount; an amortising loan charges interest on the reducing balance. The quoted rates are not comparable.

Does it handle negative rates?

The arithmetic runs, but the meaning of a negative interest rate is a policy question, not a mathematical one.

How this number is produced

The calculation is I = P × R × T ÷ 100, with T in years, following the simple interest formula. The formula is repeated here so the result can be checked by hand rather than taken on trust.

This is a calculator, not advice. No clinician, accountant or adviser has reviewed it, and it cannot see your circumstances. For anything involving health, a loan, a tax filing or a religious obligation, confirm the figure with a qualified professional or the authority that publishes the rule.

Keep going