About this site

This site is a free, no-sign-up compound interest calculator built by an independent developer who makes small, focused web tools. The goal is simple: answer “what will my savings grow to?” with transparent, verifiable math instead of a black box.

Accuracy principles

• Standard formulas only. The lump-sum growth uses FV = P(1 + r/n)^nt; recurring deposits use the ordinary-annuity formula FV = PMT × ((1 + i)^N − 1) / i, with deposits at the end of each period. Both are written out on every page so you can check the work.
• Tested code. The calculation engine ships with an automated test suite that checks hand-verifiable textbook values (for example, $10,000 at 5% compounded annually for 10 years must equal $16,288.95) and cross-checks the closed-form formulas against a period-by-period simulation to the cent.
• No fabricated numbers. Every figure in the articles on this site is produced by the same tested engine that powers the calculator. Where a real-world value is inherently uncertain — future interest rates, inflation, market returns — the text says so instead of pretending precision.
• Known simplifications, stated openly. The model assumes a constant rate, a 365-day year for daily compounding, reinvested interest, and no taxes, fees or withdrawals. Real accounts differ, so treat results as estimates.

What this site is not

It is not financial advice, and it does not predict returns — no calculator can. Interest rates change, investment returns are not guaranteed, and past averages do not promise future results. For decisions that matter, verify the numbers against your own account terms or a qualified professional.

Privacy by architecture

Everything runs in your browser. There is no backend, no account, and nothing you type is transmitted or stored — see the privacy policy for details.

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