Compound Interest Calculator
Use this free online compound interest calculator to see how your money grows over time with different compounding frequencies. Calculate total returns for savings and investments.
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Formula
How it works: A = final amount, P = principal, r = annual rate (decimal), n = compounds per year, t = years.
Review and Methodology
This calculator runs locally in your browser. Inputs are converted into the units required by the formula, and the result is paired with supporting references so you can verify the method before using it for planning or estimates.
Worked Example
What Is Compound Interest?
Compound interest is interest calculated on both the initial principal and the accumulated interest from previous periods. This creates an exponential growth effect often called "interest on interest." Albert Einstein reportedly called compound interest the "eighth wonder of the world" because of its powerful wealth-building potential.
- $1,000 at 5% compounded annually grows to $1,628 in 10 years (vs $1,500 with simple interest)
- More frequent compounding (monthly vs annually) produces slightly higher returns
- The Rule of 72: divide 72 by the interest rate to estimate years to double your money
- Starting early makes a dramatic difference: investing $1,000 at age 20 at 7% becomes $21,002 at age 65
Compound interest is the foundation of long-term investing, savings accounts, mortgages, and credit card debt. Understanding it helps you make better financial decisions whether you are saving, investing, or borrowing.
You can also calculate changes using our Simple Interest Calculator or ROI Calculator.
Frequently Asked Questions
What is compound interest?
Interest calculated on both the initial principal and the accumulated interest from previous periods. This means your interest earns interest, creating exponential growth over time.
How does compounding frequency affect returns?
More frequent compounding results in slightly higher returns because interest is calculated and added to the balance sooner, earning interest on itself faster. Daily compounding beats monthly, which beats quarterly, and so on.
What is the Rule of 72?
A quick mental math shortcut: divide 72 by the interest rate to estimate how many years it takes to double your money. At 6%, it takes about 72/6 = 12 years. At 8%, about 72/8 = 9 years.
How does compound interest differ from simple interest?
Simple interest only calculates on the original principal and grows linearly. Compound interest calculates on principal plus accumulated interest and grows exponentially. Over 30 years at 7%, $10,000 becomes $31,000 with simple interest but $76,123 with compound interest.
Why should I start investing early?
Because of compound interest, time is the most powerful factor. $5,000 invested at age 25 at 7% annual return grows to about $74,872 by age 65. The same $5,000 invested at age 35 only grows to $38,061. Starting 10 years earlier nearly doubles the result.
Can I embed this Compound Interest Calculator on my website?
Yes. Click the "Embed" button at the top of this page to customize the size, colors, and theme, then copy the iframe code. Paste it into any HTML page, WordPress site, or CMS. It is completely free, requires no signup, and works on all devices. You can also visit our embed guide at calculory.com/services/embed-calculators for more details.
Financial Disclaimer
This calculator is provided for informational and educational purposes only. It is not intended as financial, investment, or tax advice. Results are estimates and may not reflect your actual financial situation. Always consult a qualified financial advisor or tax professional before making any financial decisions based on these results.
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