Compound Interest Calculator

See how your money grows exponentially over time. The earlier you start, the more powerful the effect.

"My wealth has come from a combination of living in America, some lucky genes, and compound interest."

— Warren Buffett

Your Numbers

$
$
1%15%
5 years50 years

Key Insight: At 7% annual return, your money doubles approximately every 10 years. This is the Rule of 72 in action!

Final Balance

$252,111

Total Contributions

$73,000

Interest Earned

$179,111

Growth Over Time

Year 0
$1,000
Year 3
$9,219
Year 6
$19,352
Year 9
$31,846
Year 12
$47,250
Year 15
$66,241
Year 18
$89,657
Year 21
$118,526
Year 24
$154,120
Year 27
$198,004
Year 30
$252,111
Your Contributions
Total with Interest

Year-by-Year Breakdown

YearBalanceContributedInterest
0$1,000$1,000$0
2$6,286$5,800$486
4$12,364$10,600$1,764
6$19,352$15,400$3,952
8$27,388$20,200$7,188
10$36,627$25,000$11,627
12$47,250$29,800$17,450
14$59,464$34,600$24,864
16$73,509$39,400$34,109
18$89,657$44,200$45,457
20$108,224$49,000$59,224
22$129,573$53,800$75,773
24$154,120$58,600$95,520
26$182,344$63,400$118,944
28$214,797$68,200$146,597
30$252,111$73,000$179,111

The Math Behind It

Basic Compound Interest Formula

A = P(1 + r/n)nt

  • A = Final amount (what you end up with)
  • P = Principal (your starting amount)
  • r = Annual interest rate (as a decimal, so 7% = 0.07)
  • n = Number of times interest compounds per year (12 for monthly)
  • t = Time in years

With Regular Contributions

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

  • PMT = Regular payment/contribution amount
  • The second part calculates the future value of all your regular contributions

Simple Example: $1,000 at 7% for 10 years = $1,000 × (1.07)10 = $1,967

Rule of 72 (Quick Mental Math)

Years to Double = 72 / Interest Rate

At 6%: 12 years
At 8%: 9 years
At 10%: 7.2 years

Understanding Compound Interest

Why It Matters

Compound interest means you earn interest not just on your original investment, but also on all the interest you've already earned. It's interest on interest, and it's incredibly powerful over long periods.

Warren Buffett made 99% of his wealth after age 50, not because he suddenly got better at investing, but because compound interest had decades to work its magic.

The Three Keys

  • 1Start early. Time is your greatest asset. Even small amounts grow enormously.
  • 2Be consistent. Regular contributions matter more than timing the market.
  • 3Don't interrupt. Every withdrawal or pause resets your compounding progress.