Compound Interest Calculator

See how your money can grow with compound interest. Enter an initial investment, annual interest rate, time horizon and optional monthly contribution to project your future value and total interest earned.

Currency

Initial investment

= 10,000 $Annual interest rate

Years

Monthly contribution

Compounding

Future value

$144,572.72

Total contributed$58,000.00

Interest earned$86,572.72

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How it works

A is the future value, P the initial principal, r the annual rate, n the number of compounding periods per year, t the years, and PMT the contribution per period. Compounding means you earn interest on previously earned interest.

A = P(1 + r/n)^(nt) + PMT · ((1 + r/n)^(nt) − 1) ÷ (r/n)

Worked examples

10,000 at 7% compounded monthly for 20 years
Peter left 10,000 invested for twenty years without adding to it.
10,000 invested at 7% compounded monthly grows to about 40,387 after 20 years, even with no further contributions.
The same account with 200 added every month
Salma, adding 200 a month to the same account — which is where most of the final balance comes from.
Adding 200 a month to the same 10,000 at 7% compounded monthly for 20 years reaches 144,573, against 40,387 with no contributions — the payments themselves account for the difference.
Simple interest on the same 10,000 for 20 years
Rehema, weighing a simple-interest offer against the compounded account Peter used.
Simple interest of 7% a year on 10,000 pays 700 each year and ends at 24,000 after 20 years, where monthly compounding reaches about 40,387. The gap of about 16,387 is interest earned on interest, which is what compounding adds at the same rate over the same term.

What this assumes, and where it does not apply

What it assumes

Interest compounds at the frequency you select, and any regular contribution is added at the end of each period.
The rate stays constant for the whole term.
The rate is a nominal annual figure applied as the rate divided by the compounding periods, so the effective annual growth is slightly higher than the number entered when compounding is more frequent than yearly.

Where the result does not apply

A rate quoted as an annual nominal figure with monthly compounding gives a different result from the same rate compounded annually.
Interest tax, account fees and inflation are not modelled - see the inflation calculator for what a future amount is worth in today's money.
Withdrawals are not modelled, so an account from which money is taken out part way through will not match a figure built only from deposits and interest.

Frequently asked questions

What is compound interest?

Compound interest is interest earned on both your original principal and the interest that has already accumulated.

How does compounding frequency matter?

More frequent compounding (e.g., monthly vs annually) yields slightly higher returns at the same rate.

What is the difference between simple and compound interest?

Simple interest is paid only on the principal, while compound interest also pays on accumulated interest.

Why is my bank's effective rate higher than the quoted rate?

Because compounding adds interest to the balance during the year, so the growth over twelve months is slightly more than the quoted annual rate. A rate compounded monthly therefore has a higher effective annual rate than the same rate compounded yearly.

Results are estimates provided for information only and do not constitute financial, legal or tax advice. Consult a qualified professional before making financial decisions.

Delta Tech Solutions prepared this page. No external tax, accounting or legal professional reviewed it — the figures were checked against the sources listed above, and you should confirm anything you rely on with the authority that sets it.

Sources: US Securities and Exchange Commission — Investor.gov: compound interest

Maintained by David M at Delta Tech Solutions · Figures last checked 10 October 2026 · Next check due 10 April 2027

Read the guide: VICOBA and SACCOS Group Loan Interest →

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Compound Interest Calculator

How it works

Worked examples

10,000 at 7% compounded monthly for 20 years

The same account with 200 added every month

Simple interest on the same 10,000 for 20 years