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
Your Results
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.
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Frequently Asked Questions
What is compound interest?
Compound interest is interest earned on both your original principal and on previously earned interest. Unlike simple interest (which only applies to the principal), compound interest makes your money grow exponentially over time. The longer you invest, the more powerful the compounding effect becomes.
What is the Rule of 72?
The Rule of 72 is a quick way to estimate how long it takes to double your money. Divide 72 by your annual interest rate. At 8% returns, your money doubles in about 9 years (72 / 8 = 9). At 12%, it doubles in 6 years. This rule works best for rates between 6% and 10%.
Does compounding frequency matter?
More frequent compounding (daily vs annually) earns slightly more interest, but the difference is small. For example, $10,000 at 5% for 10 years earns $6,289 compounded annually vs $6,487 compounded daily, a difference of only $198. Your contribution amount and time horizon matter far more.