Compound Interest Calculator
See how a deposit grows over time as interest compounds at any frequency.
Try an example
$18,193.97
About this calculator
What Is Compound Interest?
Compound interest is interest that earns interest. Instead of paying you only on your original deposit, each period's interest is added to the balance, and the next period's interest is calculated on that larger amount. Over short stretches the difference from simple interest is small; over decades it becomes dramatic. This compound interest calculator shows how a starting amount grows over time at your chosen rate and compounding frequency.
The Compound Interest Formula
A = P × (1 + r/n)n·t, where A is the final amount, P is the principal, r is the annual interest rate as a decimal, n is how many times per year interest compounds, and t is the number of years. The compound interest earned is simply A − P. When you add money regularly, each contribution grows with the same rule from the day it goes in.
Worked Example
$10,000 deposited at 6% annual interest, compounded monthly, grows to $18,193.97 after 10 years — $8,193.97 in interest, more than 80% growth on the original deposit, without adding another dollar yourself.
How Compounding Frequency Matters
The more often interest is added, the faster the balance grows — but the gains from higher frequency flatten out quickly. Moving from annual to monthly compounding makes a visible difference; moving from daily to continuous compounding barely registers. Common schedules are annual, semi-annual, quarterly, monthly and daily. Banks usually compound savings accounts daily or monthly, while many bonds pay semi-annually.
Three Levers That Drive Growth
- Time — the single most powerful lever. Money left alone for 30 years grows far more than twice what it does in 15, because the later years compound on a much bigger base.
- Rate — even one extra percentage point adds up across a long horizon.
- Contributions — steady deposits give compounding more to work with every period.
Compound Interest Works Against Debt Too
The same math that grows savings makes unpaid balances grow. Credit cards and other revolving debt often compound daily or monthly, so interest accumulates on interest you have not yet paid. That is one reason paying more than the minimum matters so much.
The Rule of 72
For a quick estimate of how long it takes to double your money, divide 72 by the annual rate of return. At 6% it takes about 12 years; at 9%, about 8. It is an approximation, but it is accurate enough for back-of-the-envelope planning.
Compound vs. Simple Interest
With simple interest, only the original principal earns interest, so growth is a straight line. Compound interest grows along a curve that gets steeper over time. If you only need flat-rate interest — for example on some short-term loans — use the Simple Interest Calculator; to work toward a goal, try the Future Value Calculator.
Worked example
A $10,000 deposit at 6% APR, compounded monthly for 10 years, grows to $18,193.97 — $8,193.97 in interest earned, more than a simple-interest deposit would earn on the same terms.
Frequently asked questions
What does compounding frequency change?
More frequent compounding (daily vs. annually) earns slightly more, since interest starts earning its own interest sooner — the difference is usually small at typical rates.
What's the formula behind this?
A = P(1 + r/n)^(nt) — principal, annual rate, compounds per year, and years.
How is this different from simple interest?
Simple interest only accrues on the original principal; compound interest also earns on previously accumulated interest, so it grows faster the longer the money sits.
Does this account for additional contributions?
No — this calculates the growth of a single lump-sum deposit. Regular contributions would need a separate running calculation.
