Compound Interest Calculator
See how money grows with compound interest — any frequency, optional periodic contributions, Rule of 72.
Final amount
US$221,964.02
Total interest
US$121,964.02
Contributions
US$100,000.00
Doubles in (Rule of 72)
9 yr
📐 About This Calculator
Compound interest earns interest on both your principal and previously earned interest. The more frequently it compounds, the faster it grows.
🔢 Your calculation, step by step:
- 1.Your input:
P = 100,000, r = 8%, t = 10 yr, compounded 12×/yr - 2.Step 1 — apply formula:
A = P × (1 + r/n)^(n×t) - 3.Step 2 — result:
A = 221,964.02
Variable Definitions:
- • P = Principal (starting amount)
- • r = Annual interest rate
- • n = Compounding periods per year
- • t = Number of years
✅ Best used for:
- • Savings and FD growth
- • Investment projection
- • Understanding compounding frequency
⚠️ Limitations:
- • Assumes a fixed rate for the whole period
- • Does not model taxes on interest
📖 How Compound Interest is Calculated
Compound vs simple interest
Simple interest is charged only on the principal; compound interest is charged on the growing balance, so it pulls ahead more and more over time.
Why frequency matters
Daily compounding produces slightly more than yearly for the same rate, because interest is added to the balance more often.
The Rule of 72
Divide 72 by the annual rate to estimate how many years it takes your money to double — e.g. at 8%, about 9 years.