Compound Interest Calculator
Compound interest is interest earning interest. Instead of paying out only on your original deposit, each period's interest is added to the balance and earns interest itself, so the balance grows faster the longer you leave it. This compound interest calculator shows how a one-time lump sum grows from the starting amount, the annual rate, how often interest compounds, and the number of years. The more frequently interest compounds and the longer the time horizon, the larger the gap between what you put in and what you end with — which is why starting early matters so much.
Calculate
Default result: $1,647.01
Compound Interest Calculator · Materials
calculators.dev
Future value
1000 × 5 × 12 × 10
Shopping list
- Interest earned
- $647.01
Est. total
$1,647.01
Estimate — confirm w/ supplier · calculators.dev
This calculator provides estimates for general informational purposes only and is not financial, investment, tax, or legal advice. Results are projections based on the figures you enter and the stated assumptions, and actual outcomes will differ. Consult a qualified financial professional before making borrowing, saving, or investment decisions.
Reviewed by the calculators.dev team · Last updated 2026-06-24
Formula reviewed against Investor.gov Compound Interest Calculator — U.S. SEC reference for future value
How to calculate
Enter the starting amount, the annual interest rate, how many times a year interest compounds (12 for monthly), and the number of years. The calculator applies the compound-interest formula, dividing the annual rate by the compounding frequency and raising it to the total number of periods. For $1,000 at 5% compounded monthly over 10 years, the future value is about $1,647.01 and the interest earned is $647.01. Try changing the years to see how growth accelerates over longer horizons.
FV = P(1 + r/n)^(n·t). FV is the future value, P is the starting amount, r is the annual rate as a decimal, n is the number of times interest compounds per year, and t is the number of years. Interest earned is FV − P. More frequent compounding (larger n) and a longer horizon (larger t) both increase the future value.
Example calculation
A $1,000 deposit at a 5% annual rate compounded monthly for 10 years grows to about $1,647.01. Compounding monthly means interest is added 120 times, and each addition earns interest of its own, so the $647 of growth is more than the $500 simple interest would have produced over the same period.
- futureValue
- $1,647.01
- interestEarned
- $647.01
Assumptions
- The rate is fixed and interest is reinvested at the same rate each period — real returns vary.
- No deposits or withdrawals are made after the initial amount; for regular contributions, use the investment growth calculator.
- Taxes and fees are not deducted; in a taxable account, both would reduce the net growth.
Common mistakes
- Confusing compounding frequency with the rate — compounding more often raises growth slightly, but the annual rate is the bigger driver.
- Underestimating time: doubling the years far more than doubles the interest, because growth compounds.
- Comparing compound and simple interest at short horizons, where the difference is small and the advantage of compounding is easy to miss.
Frequently asked questions
What is compound interest?
Interest calculated on both your original amount and the interest already added. Because each period's interest earns interest of its own, the balance grows faster over time than with simple interest.
Does compounding frequency matter much?
It helps, but less than people expect. Going from annual to monthly compounding at 5% over 10 years adds only a small amount. The rate and the number of years matter far more.
How is this different from the investment calculator?
This page grows a single lump sum. The investment growth calculator also adds regular monthly contributions, which is how most people actually build savings.
Why does starting early help so much?
Compounding rewards time. Money invested earlier has more periods to earn interest on interest, so an early start can outweigh larger contributions made later.