Compound Interest Calculator
Project the future value of savings, mutual funds, and index funds — with the maths behind it.
- 1Compound interest formulaFREEA = P(1 + r/n)^(nt) + PMT·[((1 + r/n)^(nt) − 1) / (r/n)]
- 2Plug in the variables
- 3Growth factor (1 + r/n)^(nt)
- 4Interest on the starting balance
- 5Interest on monthly contributions
- 6Final value (without annual increase)
Growth over time
Year by year
| Year | Contributed | Total contributed | Interest | Total value |
|---|---|---|---|---|
| 0 | $10,000 | $10,000 | $0 | $10,000 |
| 1 | $12,000 | $22,000 | $1,115 | $23,115 |
| 2 | $12,000 | $34,000 | $2,064 | $37,179 |
| 3 | $12,000 | $46,000 | $3,080 | $52,259 |
| 4 | $12,000 | $58,000 | $4,170 | $68,430 |
| 5 | $12,000 | $70,000 | $5,339 | $85,769 |
| 6 | $12,000 | $82,000 | $6,593 | $104,362 |
| 7 | $12,000 | $94,000 | $7,937 | $124,299 |
| 8 | $12,000 | $106,000 | $9,378 | $145,677 |
| 9 | $12,000 | $118,000 | $10,924 | $168,601 |
| 10 | $12,000 | $130,000 | $12,581 | $193,181 |
| 11 | $12,000 | $142,000 | $14,358 | $219,539 |
| 12 | $12,000 | $154,000 | $16,263 | $247,802 |
| 13 | $12,000 | $166,000 | $18,306 | $278,108 |
| 14 | $12,000 | $178,000 | $20,497 | $310,605 |
| 15 | $12,000 | $190,000 | $22,846 | $345,452 |
| 16 | $12,000 | $202,000 | $25,365 | $382,817 |
| 17 | $12,000 | $214,000 | $28,066 | $422,884 |
| 18 | $12,000 | $226,000 | $30,963 | $465,846 |
| 19 | $12,000 | $238,000 | $34,069 | $511,915 |
| 20 | $12,000 | $250,000 | $37,399 | $561,314 |
About this calculator
Compound interest is the effect of earning interest on both your original principal and on previously earned interest — the self-reinforcing exponential growth often called "the superpower of saving." Common in mutual funds, index funds, and high-yield savings accounts. This is a maths tool, not financial advice.
How compound interest works
The formula is A = P(1 + r/n)^(nt) + PMT·[((1 + r/n)^(nt) − 1) / (r/n)]. P is the starting balance; PMT the monthly contribution; r the annual return rate (as a decimal); n the number of compounding periods per year (12 for monthly); t the number of years. The first term grows your starting balance by the compound factor; the second term grows the stream of monthly contributions. The reason the curve bends upward is that interest earned in earlier years itself earns interest in later years — small early differences in rate, time, or starting age make outsized differences at the end.