Money & savings

Compound Interest Calculator

See how an initial deposit and regular contributions could grow. Compare investment return assumptions and explore the effect of time and compounding.

Your inputs

Build your estimate

Initial deposit ($) Recurring contribution ($) Contribution frequency Contribution timing Annual nominal interest / return (%) Compounding frequency Investment period (whole years)

Enter a nominal annual rate, not APY. For an effective annual return assumption or APY, select annual compounding. Negative rates model a constant loss. Enter 0 for no contribution or no growth.

Compare other return assumptions (optional)

Alternative annual rate 1 (%)Alternative annual rate 2 (%)

All scenarios use the same deposit, contributions, timing, period and compounding frequency.

Estimated balance over time

Compare your contributions with each return assumption. Exact yearly values are available in the table below.

Return assumption comparison

All amounts are estimates in US dollars.
Annual nominal rate	Effective annual rate	Contributions	Interest / growth	Ending balance

Year-by-year estimate

How this compound interest calculator works

Compound interest is growth on both your original money and earlier growth. This investment growth calculator assumes a constant annual nominal rate and reinvests all growth.

With annual nominal rate r as a decimal and n compounding periods per year, the equivalent monthly rate is i = (1 + r/n)^(n/12) − 1. Without contributions, the balance after t years is P × (1 + r/n)^(n×t).

For monthly contributions, each month uses B = B × (1+i) + C for end timing, or B = (B+C) × (1+i) for beginning timing. Annual contributions occur once, at the start or end of each investment year. Total contributions include the initial deposit; growth is the ending balance minus those contributions.

When deposit and compounding schedules differ, we use equivalent fractional-period growth. Daily compounding assumes 365 equal days per year; months are one-twelfth of a year. This is a mathematical projection, not a simulation of a bank's interest-crediting or calendar rules. Amounts are calculated without monthly rounding and displayed to the nearest cent.

A simple example

A $10,000 deposit at a 6% nominal annual rate, compounded monthly for 10 years with $200 added at each month-end, grows to approximately $50,969.84. Contributions total $34,000 and estimated growth is $16,969.84.

Questions about compound interest

Does contribution timing matter?

Beginning-of-period contributions have longer to grow. At positive rates they produce a higher ending balance; at negative rates they are exposed to losses for longer.

Is the annual rate the same as APY?

No. APY already includes compounding. To model a quoted APY, enter it as the rate and select annual compounding. Selecting monthly compounding with that same rate would compound it again.

Are these investment returns guaranteed?

No. The scenarios are assumptions, not forecasts or probabilities. A fixed rate cannot represent market volatility or the order of actual returns. Compare several assumptions and consider taxes, fees and inflation separately.

Learn about compounding with the SEC Investor.gov compound interest calculator.