Compound Interest Calculator: Turn Time Into Money

Published August 2026 | 6 min read

Einstein allegedly called compound interest the "8th wonder of the world." Whether he said it or not, the math is undeniable. Use our free compound interest calculator to see how much your money can grow.

Compound vs. Simple Interest

Simple interest: You earn interest on the principal only.

Compound interest: You earn interest on your interest. That's the magic.

Example: $10,000 at 7% for 30 years:

Simple interest: $31,000 total
Compound interest: $76,123 total

Compound interest more than doubles your return.

APY vs. APR: Know the Difference

APR — Annual Percentage Rate (nominal rate)
APY — Annual Percentage Yield (includes compounding)

A 5% APR compounded monthly = 5.12% APY. A 5% APR compounded daily = 5.13% APY. Small differences add up over decades.

The Rule of 72

Quick mental math: Divide 72 by your interest rate to see how many years it takes to double your money.

At 6%: 72 ÷ 6 = 12 years to double
At 10%: 72 ÷ 10 = 7.2 years to double

Real-World Examples

Scenario	Final Amount
$500/month at 7% for 20 years	$260,000
$1,000/month at 10% for 30 years	$2.17 million
$10,000 lump sum at 8% for 40 years	$217,000

💡 Find the Best Savings Rate

Online banks offer 4-5% APY right now — 10x more than big banks.

Compare High-Yield Savings →

The Bottom Line

Time is your biggest asset. Start early, even with small amounts. Use our compound interest calculator to experiment with different rates, contributions, and timeframes.