Compound Interest Calculator
Enter the initial principal, monthly contribution, interest rate, and time period to see the final value, total invested, and total interest.
Total invested$3,400.00
Total interest$263.33
Month-by-month evolution
| Month | Invested | Interest | Balance |
|---|---|---|---|
| 1 | $1,200.00 | $10.00 | $1,210.00 |
| 2 | $1,400.00 | $22.10 | $1,422.10 |
| 3 | $1,600.00 | $36.32 | $1,636.32 |
| 4 | $1,800.00 | $52.68 | $1,852.68 |
| 5 | $2,000.00 | $71.21 | $2,071.21 |
| 6 | $2,200.00 | $91.92 | $2,291.92 |
| 7 | $2,400.00 | $114.84 | $2,514.84 |
| 8 | $2,600.00 | $139.99 | $2,739.99 |
| 9 | $2,800.00 | $167.39 | $2,967.39 |
| 10 | $3,000.00 | $197.06 | $3,197.06 |
| 11 | $3,200.00 | $229.04 | $3,429.04 |
| 12 | $3,400.00 | $263.33 | $3,663.33 |
How it works
Compound interest is calculated on the accumulated balance (principal + prior interest), not just the initial principal — which is why growth accelerates over time, unlike simple interest. The formula used is FV = P × (1+i)^n + A × (((1+i)^n − 1) / i), where P is the principal, A is the monthly contribution, i is the monthly rate, and n is the number of months. When the rate you enter is annual, it's converted to its true equivalent monthly rate with (1+annual_rate)^(1/12) − 1 — the correct compound conversion, not a simple division by 12.