Compound & Simple Interest Calculator

Enter your principal, rate and duration to see projected growth, all computed locally, nothing uploaded.

How Compound & Simple Interest Calculator works

Compound interest is one of the most powerful forces in personal finance, your interest earns interest, so even modest savings grow significantly over time. This calculator projects the future value of a lump sum or loan, optionally topped up with monthly contributions, at any compounding frequency from daily to annual. A simple-interest mode is included for flat-rate cases.

Model any scenario in real time, from a 30-year retirement fund to a 36-month car loan. The projection is a mathematical estimate that ignores taxes, fees and inflation, so treat it as a guide rather than a guaranteed return.

Frequently asked questions

Is my data sent to any server?

No. All calculations happen locally in your browser. No inputs or results leave your device, and it works offline once loaded.

Compound vs simple interest?

Simple interest is on the original principal only. Compound interest is recalculated each period so interest earns interest, producing accelerating growth.

How are monthly contributions handled?

Via the future-value-of-annuity formula at the equivalent monthly rate (an approximation). Results are estimates, not guaranteed returns.

Is this financial advice?

No. It gives mathematical estimates from your inputs and ignores taxes, fees and inflation. Consult a qualified adviser before deciding.

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