Finance

Compound Interest Calculator

Free compound interest calculator: see how your investment grows with compound interest and regular contributions. Enter principal, rate, term, and monthly deposits.

YOUR WORKSPACEFree to use. No sign-up.

Initial investment

Annual rate (%)

Years

Monthly contribution

Compounds/year

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Deep dive guides

A LITTLE CONTEXT · 3 MIN READHow Compound Interest Works

All 10 related guides

How Compound Interest Works — A plain-English guide to compound interest: the formula, compounding frequency, and why it grows money faster than simple interest.
Compound Interest Comparison: How to Compare Savings Plans — A plain-English guide to comparing compound-interest scenarios: the shared formula, what to vary, ordinary annuity vs annuity due, and effective APY.
The 4% Rule Explained: A Safe Retirement Withdrawal Rate — A plain-English guide to the 4% rule: where it comes from, why 4% is considered safe, how inflation adjustments work, and when it breaks.
APR vs APY: Why They Differ — APR vs APY: why the same interest rate produces two different annual numbers, the (1+r/n)^n − 1 bridge formula, and who quotes which and why.
How CAGR Reveals Real Growth — The compound annual growth rate explained: why you can't divide total return by years, average vs geometric returns, CAGR vs ROI, and the rule of 72.
How Investment Fees Compound Against You — Where fees hide, why a 1% fee removes about a quarter of a 30-year balance, how the cost scales with time, and which costs you can actually control.
Simple vs Compound Interest: Why the Difference Compounds — How simple and compound interest diverge: the year-by-year gap, why the difference itself compounds, doubling time, and where each formula applies.
Savings Goals: How the Month-by-Month Plan Finds Your Finish Line — Interest first, deposit after: the monthly loop that decides when — or whether — you hit your goal.
ROI Explained: Simple Return, Annualized Return and the Time Trap — Profit over cost is easy; making returns comparable across different holding periods is where annualizing comes in.
Retirement Savings Math: Projecting Your Nest Egg — The two future values behind a retirement projection, the return assumption that dominates it, and how to invert the math for a required contribution.

How compound interest calculator works

Compound interest is interest earned on both your initial principal and the interest that has already accumulated. It is the most powerful force in investing: the longer your money compounds, the faster it grows. This calculator uses the standard compound interest formula A = P(1 + r/n)^(nt), where P is principal, r is the annual rate, n is compounding frequency, and t is years.

You can also add regular contributions (monthly deposits) to see how consistent saving accelerates growth. The calculator computes the future value of your principal plus the future value of an annuity (your contributions), then shows the total balance, total amount you contributed, and total interest earned.

For example, if you invest 10,000 at 7% compounded monthly for 10 years while contributing 100 per month, your balance grows to about 37,405. The interest earned (15,405) exceeds your total contributions of 22,000 because of compounding. Try different rates and timeframes to see the dramatic effect of compounding over longer periods.

Frequently asked questions

What is compound interest?

Compound interest is interest calculated on both the initial principal and the accumulated interest from previous periods. This means your money grows faster over time because you earn interest on your interest, not just on your original deposit.

How is compound interest calculated?

The formula is A = P times (1 + r/n)^(nt), where P is the principal, r is the annual interest rate, n is the number of times interest is compounded per year, and t is the number of years. The calculator applies this automatically.

How do regular contributions affect growth?

Regular contributions add to your principal each period, so they also compound. Even modest monthly deposits can dramatically increase your final balance because each contribution starts compounding immediately.

What compounding frequency should I use?

Monthly compounding (12 times per year) is common for savings accounts. Daily compounding (365) gives slightly more. The more frequently interest compounds, the more you earn. The calculator defaults to monthly.

What is the difference between the rate and the APY?

The annual rate is the nominal figure before compounding; the APY (annual percentage yield) is what you actually earn once interest compounds within the year. At 6% compounded monthly the APY is about 6.17% — the calculator reports the APY so you can compare offers quoted at different frequencies on equal footing.

Compound Interest Calculator

Deep dive guides

How compound interest calculator works

Frequently asked questions

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