All Calculators

Compound Interest Calculator

See the power of compound interest. Calculate how your money grows over time with regular contributions.

Investment Details

$
$
%

Historical stock market avg: ~7-10%

years

Enter your investment details

to see how your money grows

Compound Interest

Compound interest is when you earn interest on both your original investment and on the interest you've already earned. It's often called the "eighth wonder of the world" because small, consistent investments can grow to enormous sums over time.

How to Use

  1. 1 Enter your starting amount (what you have now).
  2. 2 Enter how much you'll add each month.
  3. 3 Set your expected annual return rate.
  4. 4 Choose how long you'll invest and see your future wealth.

FAQ

What's a realistic return rate?

The S&P 500 has historically returned ~10% annually before inflation, ~7% after inflation. High-yield savings accounts offer 4-5% currently. Be conservative in estimates.

Daily vs monthly compounding?

More frequent compounding means slightly higher returns, but the difference is small. Daily compounding at 7% yields about 0.1% more per year than monthly. Focus on the rate, not frequency.

What about taxes?

This calculator shows pre-tax growth. In taxable accounts, you'll owe taxes on gains. Use tax-advantaged accounts (401k, IRA, Roth) to let compound interest work uninterrupted.

What's the Rule of 72?

Divide 72 by your interest rate to estimate how many years it takes to double your money. At 7% return: 72 ÷ 7 = ~10.3 years to double. At 10%: ~7.2 years.

Why start early?

Time is the most powerful factor. Someone who invests $5,000/year from age 25-35 (10 years) will often have more at 65 than someone who invests $5,000/year from 35-65 (30 years). Start now.

Calculator Limitations

Assumes constant returns (reality is volatile). Doesn't account for taxes, inflation, or fees. Investment returns are not guaranteed. Past performance doesn't predict future results.