GWN Tools · Calculators

Compound Interest Calculator

See how your money grows over time with compound interest and optional monthly contributions.

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%
$/mo
years
$0
projected final balance
$0
Total contributions
$0
Interest earned

Monthly compounding is used. Estimates only — not financial advice. Verify with your lender/advisor.

How a compound interest calculator works

A compound interest calculator projects how your money grows when interest is earned on both your principal and previously earned interest, including any regular monthly contributions you add along the way.

How is compound interest calculated?

With regular contributions, future value is A = P x (1 + i)^n + PMT x (((1 + i)^n - 1) / i), where P is the starting principal, PMT is the periodic contribution, i is the periodic interest rate, and n is the number of periods. This calculator compounds monthly. Estimates only, not financial advice.

What is the difference between compound and simple interest?

Simple interest is earned only on the original principal. Compound interest is earned on the principal plus all previously earned interest, so your balance grows faster over time as the interest itself starts earning interest.

Does compounding frequency matter?

Yes. The more often interest compounds, the more you earn at the same annual rate. This tool uses monthly compounding; daily compounding would yield slightly more and annual compounding slightly less.