Compound Interest Calculator
Future value of a lump sum that compounds on a fixed schedule. Figures stay on this device. They are not a forecast or advice.
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How to calculate compound interest
- Enter principal, annual rate, years, and compounding frequency.
- Optional: a contribution at each compounding date, at the start or end of the period.
- Read future value, interest, and effective annual rate.
- Figures are informational, not investment advice.
Compound interest
Future value of a lump sum with periodic compounding
| Formula | A = P (1 + r / n) ^ (n t) |
|---|---|
| P | Principal |
| r | Nominal annual rate as a decimal |
| n | Compounding periods per year |
| t | Time in years |
What compound interest is
Compound interest adds interest to the principal, then later periods earn interest on that new total. This page uses a fixed nominal annual rate and a fixed compounding schedule. It does not add deposits, fees, or tax.
How this page computes
Future value is P (1 + r / n) ^ (n t). Interest earned is future value minus principal. Effective annual rate is (1 + r / n) ^ n - 1. Daily compounding uses 365 periods per year, not a bank day-count convention.
Not a quote or advice
Banks, brokers, and tax rules use their own rounding, day counts, and fees. Use this page to check the textbook formula. See the disclaimer before you treat a figure as a plan. Other money pages live under finance calculators.