Compound Interest: How Your Money Grows Over Time
7 min read · Updated June 2026
Albert Einstein allegedly called compound interest the "eighth wonder of the world." Whether he said it or not, the math is undeniable: compound interest is the single most powerful force in personal finance.
Simple vs Compound Interest
- Simple interest — You earn interest only on the principal. $10,000 at 7% for 30 years = $10,000 + $21,000 = $31,000
- Compound interest — You earn interest on the principal AND the accumulated interest. $10,000 at 7% for 30 years = $76,123
The difference: $45,123 — more than 4× your original investment, just from compounding.
The Compound Interest Formula
A = P × (1 + r/n)^(n×t)
A = Final amount, P = Principal, r = Annual rate, n = Compounding frequency, t = Years
How Compounding Frequency Matters
$100,000 at 7% for 30 years:
| Frequency | Final Amount |
|---|---|
| Annually | $761,230 |
| Quarterly | $769,970 |
| Monthly | $772,350 |
| Daily | $773,180 |
The Rule of 72
Divide 72 by your interest rate to estimate how many years it takes to double your money:
- At 6%: 72 ÷ 6 = 12 years to double
- At 8%: 72 ÷ 8 = 9 years to double
- At 10%: 72 ÷ 10 = 7.2 years to double
Inflation: The Silent Killer
A 7% return with 3% inflation means your real return is only ~4%. After 30 years at 7% nominal, $100,000 grows to $761,230 — but in today's dollars, that's only about $314,000 of purchasing power.
🧮 Calculate your Compound Interest
Use our Compound Interest Calculator to see your investment growth with monthly contributions, inflation adjustment, and a year-by-year schedule.
The Bottom Line
- Start early — time is more important than the amount invested
- Compound interest turns small, consistent contributions into large sums
- Always account for inflation when planning long-term investments
- Use the Rule of 72 to quickly estimate doubling time
Disclaimer: This guide is for informational purposes only and does not constitute financial advice. Past performance does not guarantee future results.