The 8th Wonder of the World

Compound Interest
Calculator

See how your investment grows exponentially over time — with or without regular contributions.

Initial Investment ($)
$
Monthly Contribution ($)
$
Annual Return (%)
%
Time Period (Years)
Compounding Frequency
Future Value
$0.00
After 20 years at 7%
Total Deposited
—
your contributions
Interest Earned
—
compounding gains
Return Multiple
—
× initial
At 10 Years
—
halfway point
Monthly Income
—
at 4% withdrawal
Interest %
—
of total value

The Power of Compound Interest

Compound interest means you earn interest on your interest — creating exponential, not linear, growth. The longer you invest, the more dramatic the effect.

A = P(1 + r/n)^(nt) + PMT × [(1 + r/n)^(nt) − 1] / (r/n)

A = final amount · P = principal · r = annual rate
n = compounds/year · t = years · PMT = monthly contribution

Rule of 72

Divide 72 by your annual return rate to find how many years to double your money: at 7%, money doubles every ~10.3 years. At 10%, every 7.2 years.

Historical returns reference

Compound Interest FAQ
Simple interest calculates interest only on your principal. Compound interest calculates interest on the principal PLUS accumulated interest. At 7% over 20 years, $10,000 grows to $13,400 (simple) vs $38,697 (compound).
More frequent compounding = slightly more growth, but the difference is small. At 7% for 20 years on $10k: annually → $38,697 | monthly → $40,169 | daily → $40,253. The rate matters far more than compounding frequency.
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