Compound Interest Calculator
See how your investments grow over time with compound interest. Adjust your starting amount, monthly contributions, and interest rate.
Free calculator with interactive growth chart and year-by-year breakdown
Your Investment Details
Total Value After 20 Years
$302,370
Your money doubles in ~2 years
Total Contributions
$130,000
Interest Earned
$172,370
Interest Share
57%
Contributions vs Interest
Growth Over Time
Investment Scenarios
$10K Investment Growth
See how a one-time $10,000 investment grows over t...
$500/Month Investing
How much can you accumulate by investing $500 ever...
Millionaire Calculator
How long will it take you to reach $1,000,000?...
Retirement Savings Growth
Project your retirement savings with employer matc...
Savings Account Interest
Calculate growth in a high-yield savings account a...
Index Fund Growth
Project growth of a total market or S&P 500 index ...
Daily vs Monthly Compounding
Compare how compounding frequency affects your ret...
Rule of 72 Calculator
Use the Rule of 72 to estimate how long it takes t...
How Compound Interest Works
Simple vs Compound
Simple interest is calculated only on your original principal. Compound interest is calculated on your principal plus all previously earned interest. Over time, compound interest creates exponential growth while simple interest grows linearly.
The Rule of 72
Divide 72 by your annual interest rate to estimate how many years it takes to double your money. At 7%, your money doubles in about 10.3 years. At 10%, it doubles in 7.2 years. At 4%, it takes 18 years.
Time is Your Greatest Asset
Starting 10 years earlier can double your final balance even with the same monthly contribution. Someone investing $500/month from age 25 to 65 at 7% will have $1.2M. Starting at 35, they will have only $567K, less than half.
Compounding Frequency
More frequent compounding (daily vs annually) earns slightly more interest, but the difference is small. What matters far more is your contribution amount, interest rate, and time horizon. Do not obsess over compounding frequency.
Understanding Compound Interest in 2026
Compound interest is often called the eighth wonder of the world. Albert Einstein allegedly said, "He who understands it, earns it; he who doesn't, pays it." Whether investing in the stock market, saving in a high-yield account, or paying off debt, compound interest is the most powerful force in personal finance.
In 2026, high-yield savings accounts offer 4-5% APY, and the long-term average return of the S&P 500 is about 10% annually. Use this calculator to see the difference between saving in a bank account versus investing in the stock market over 10, 20, or 30 years.