Compound Interest Calculator

What is compound interest calculator?

Compound interest is the reason small, regular savings can grow into large sums over time. Each period, interest is added to the balance, and the next period's interest is paid on the larger amount.

This calculator adds a monthly deposit, which is how most people save. It shows the final balance, how much you put in yourself and how much came from interest.

How to use the compound interest calculator

1. Enter your starting amount and monthly deposit.
2. Add the expected yearly interest rate and the number of years.
3. Choose how often interest compounds and press Calculate.

How the compound interest calculator works

Each month the deposit is added. Whenever a compounding period ends, the balance is multiplied by one plus the rate divided by the number of periods per year. The year by year table records the total deposited, interest earned and balance.

Worked example

Common uses of the compound interest calculator

• Seeing how a monthly savings habit grows over ten, twenty or thirty years.
• Comparing a savings account with an investment at different rates.
• Understanding why starting early matters.
• Planning for a goal such as a home deposit or education fund.
• Learning how interest on a debt can snowball.

Tips and common mistakes

Time matters more than the exact rate. Starting five years earlier often beats a slightly higher return.

Real returns vary and are not guaranteed. Use a cautious rate and remember that inflation reduces what money can buy.

Background: what to know before you rely on it

Albert Einstein is often quoted as calling compound interest the eighth wonder of the world, though there is no proof he said it. The idea is real. When interest is added to the balance, the next period earns interest on a larger amount, so growth speeds up over time. Doubling time can be estimated with the rule of 72: divide 72 by the yearly rate to get the years needed. At 6 percent, money doubles in about 12 years. The same force works against borrowers, which is why credit card debt grows fast. Use cautious rates in projections, because returns vary and fees and inflation reduce real growth.

Private, free and fast

This tool runs entirely in your browser. What you type or choose is not uploaded to a server and is not saved after you close the page, which keeps it fast and private. It is free to use as often as you like. See more in all finance calculators, or browse the full list of tools.

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Results are for information and education. For legal, financial, medical or security decisions, check with a qualified professional. Estimates only. Confirm with your lender or accountant.