Tools · Investing

Compound Interest Calculator

See how your savings or investments grow over time, including the impact of regular monthly contributions.

$
$
%
Estimated final balance
$0
Total contributed $0
Total growth $0
Initial amount $0
Total monthly contributions $0

How this calculator works

This calculator combines two components: growth on your initial lump sum, and growth on a series of regular monthly contributions, both compounding at your selected frequency.

A = P(1 + r/n)nt

Where P is your initial amount, r is the annual interest rate, n is the compounding frequency per year, and t is time in years. Monthly contributions are calculated using the future value of a series formula and added to this base growth.

The "estimated annual return" you enter should reflect a realistic, conservative expectation — historical stock market averages, high-yield savings rates, or whatever benchmark fits your actual account type. This calculator does not account for taxes, fees, or inflation, all of which reduce real purchasing power over time.

Common questions

What return rate should I actually use?

For a high-yield savings account, use the current published APY. For long-term stock market investing, many planners use 6-8% as a conservative historical average, though actual returns vary significantly year to year and are never guaranteed.

Does this account for inflation?

No. The number shown is in nominal dollars. To estimate purchasing power in today's dollars, you'd need to subtract an assumed inflation rate from your return rate before calculating.

Why does compounding frequency matter?

More frequent compounding (monthly vs. annually) results in slightly higher growth at the same stated annual rate, because interest earned starts earning its own interest sooner.

Does this include taxes on investment gains?

No. Tax treatment depends heavily on account type (taxable brokerage, traditional retirement account, Roth account) and your individual tax situation, so this calculator shows pre-tax growth only.

This calculator provides estimates for educational purposes only and does not constitute financial or investment advice. Actual returns are not guaranteed and will vary.