Compound interest calculator

How to use

1. Enter the initial amount, the regular contribution and how often you add it, the annual rate and the number of years. Either the initial amount or the contribution can be 0.
2. Choose how often interest compounds and whether contributions are made at the start or end of each period.
3. The final balance, initial amount, total contributions and total interest appear with a year-by-year table. Use "Download CSV" to save the table.

Notes and limits

• The rate is constant for the whole period. Taxes, fees and inflation are not included.
• This is a calculation, not a forecast or a promise of investment returns.
• Periods are whole years from 1 to 100, and rates from 0 to 100%.

How it works

The nominal annual rate r is compounded m times a year (1, 2, 4, 12 or 365). The initial amount grows by (1 + r/m)^(m × years).

When contributions and compounding have different frequencies, the balance is simulated per contribution period using the equivalent rate j = (1 + r/m)^(m/p) − 1, where p is the number of contributions per year. The initial amount therefore still matches the compound interest formula exactly.

Start-of-period contributions earn interest for that period; end-of-period contributions are added after the interest.

No rounding is done along the way. Amounts are rounded to the currency's minor unit for display only, so table columns may differ by one unit when added up.

Doubling time is ln 2 ÷ ln(1 + effective annual rate); the rule of 72 (72 ÷ rate) is shown as a quick estimate.