Financial Planning

Compound Interest Calculator

See how regular saving and the power of compounding grow over time — and how much of your future balance is money you contributed versus interest earned.

Starting amount

Monthly contribution

Annual return %

Years

Compounding

Contribution raise %/yr

How this works

The calculator adds your monthly contribution to the balance and applies your annual return at the compounding frequency you choose. Because each period’s interest earns interest of its own in every period that follows, the balance grows faster the longer you stay invested.

The chart separates the two forces behind your ending balance: the money you contributed (the lower navy area) and the interest it earned (the green wedge on top). Over long horizons, interest often becomes the larger share — the tool marks the year it overtakes your deposits.

Assumptions & limitations

Returns are assumed constant every period; real returns vary and can be negative. Results are before taxes, fees, and inflation, so future dollars will not have today’s buying power. This illustrates compounding, not a prediction of any specific investment.

Methodology

Uses standard compound-interest and future-value-of-an-annuity relationships, simulated period by period so contribution increases and compounding frequency are handled exactly.

Good to know

The Rule of 72: divide 72 by your return to estimate doubling time. At 6%, money doubles about every 12 years.
Starting five years earlier often beats doubling your contribution later, because the earliest dollars compound longest.
Fees compound too. A 1% annual fee can consume a meaningful slice of a multi-decade balance.

Educational illustration only, not investment advice. Investing involves risk, including possible loss of principal.

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