Compound Interest Calculator

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See how your money grows with compound interest. Set the principal, rate, time, compounding frequency and an optional monthly contribution to get the future value. Free and instant.

$
%
per year
$ per month
Optional — leave at 0 for a lump-sum only.
Future value –
Starting balance –
Total contributions –
Total interest earned –
The principal compounds at the chosen frequency. Monthly contributions are added at the end of each month and compounded monthly. Returns are assumed constant and taxes and inflation are not included.

About Compound Interest Calculator

The Compound Interest Calculator shows how a balance grows when interest earns interest. Set the initial principal, annual rate, number of years and compounding frequency — annually, quarterly, monthly or daily — plus an optional monthly contribution, and it returns the future value.

The lump sum grows by the formula A = P × (1 + r/n)^(n×t), where r is the annual rate, n the number of compounding periods per year and t the years. Monthly contributions are added at the end of each month and then compound monthly themselves. The results break the future value into starting balance, total contributions and total interest earned.

Use this compound interest calculator with monthly contributions to project savings accounts, index-fund investing or any goal where regular deposits meet a steady return — and to see why starting early matters so much. Free and instant in your browser.

How to use Compound Interest Calculator

  1. Enter the initial principal — your starting balance.
  2. Set the annual interest rate and the number of years.
  3. Choose the compounding frequency: annually, quarterly, monthly or daily.
  4. Optionally add a monthly contribution (leave 0 for a lump sum only).
  5. Read the future value, split into starting balance, total contributions and interest earned.

Frequently asked questions

Interest calculated on both the original principal and the interest already earned. Each period’s interest joins the balance and earns its own interest next period, which makes growth accelerate over time.

A = P × (1 + r/n)^(n×t) for the principal, where r is the annual rate as a decimal, n the compounding periods per year and t the years. Monthly contributions are added at each month’s end and compounded monthly thereafter.

It helps, but modestly. At 5% over 10 years, daily compounding beats annual compounding by well under one percentage point of total return. Rate, time and contributions dominate the outcome.

Every deposit starts compounding from the month it is added, so regular contributions often end up producing more of the final balance than the original principal — especially over long horizons.

They are estimates, not financial advice. The math assumes a constant return and ignores taxes, fees and inflation; real investment returns fluctuate year to year, so treat the future value as a scenario, not a promise.
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