Compound Interest Calculators
Compound Interest Calculator
Enter a starting balance, rate, time horizon, and optional monthly contribution and CompoundLab estimates the future value, total contributions, and interest earned.
Compound interest growth estimate
Estimated future value
$145,180.47
- Starting principal
- $10,000
- Total contributions
- $58,000
- Total interest
- $87,180
Where the balance comes from
Estimate using a fixed annual rate. The principal compounds at the frequency you choose; contributions are grown month by month. Taxes, fees, and inflation are not modeled. An estimate of growth, not investment, tax, or financial advice.
About this calculator
A free compound interest calculator that projects how a starting balance grows over time at a fixed annual rate. It applies the exact compound formula P*(1+r/n)^(n*t) to your principal, then layers on an optional recurring monthly contribution grown month by month, and breaks the ending balance into total contributions versus interest earned. Everything runs in your browser. The result is an estimate that assumes a constant rate and ignores taxes, fees, and inflation — not investment, tax, or financial advice.
By variant
Questions
- Is the compound interest calculator free?
- Yes. It is free, needs no account, and calculates entirely in your browser — none of the figures you enter are uploaded or stored.
- How is compound interest calculated here?
- The starting principal grows with the standard compound formula P*(1+r/n)^(n*t), where r is the annual rate, n is compounds per year, and t is years. An optional monthly contribution is added each month and grown at the per-month rate, so the contribution result stays correct no matter which compounding frequency you pick for the principal.
- What is the difference between total contributions and interest earned?
- Total contributions is the money you actually put in — the starting principal plus every monthly contribution. Interest earned is the future value minus those contributions, i.e. the growth compounding added on top.
- Why might the result differ from my actual returns?
- The tool assumes a single fixed rate for the whole horizon and does not model taxes, account fees, variable returns, or inflation. Real-world returns fluctuate, so treat the number as a clean estimate of compounding, not a guaranteed outcome.