Compound Interest Calculator
See how your money grows over time with the power of compounding. Add regular contributions and watch the interest-on-interest effect build exponentially.
| Year | Balance | Interest |
|---|---|---|
| Yr 1 | $13,201 | +$801 |
| Yr 2 | $16,634 | +$1,033 |
| Yr 3 | $20,315 | +$1,281 |
| Yr 4 | $24,262 | +$1,547 |
| Yr 5 | $28,495 | +$1,832 |
| Yr 6 | $33,033 | +$2,138 |
| Yr 7 | $37,900 | +$2,466 |
| Yr 8 | $43,118 | +$2,818 |
| Yr 9 | $48,714 | +$3,196 |
| Yr 10 | $54,714 | +$3,600 |
How compound interest works
With simple interest, you earn returns only on your original investment. With compound interest, every period's earnings get added to your balance — and the next period you earn returns on that larger amount. The effect is slow at first, then dramatically accelerates.
A $10,000 investment at 7% p.a. for 30 years:
The Rule of 72
Divide 72 by your annual return rate to estimate how many years it takes to double your money. At 7% p.a., your money doubles roughly every 10 years (72 ÷ 7 = 10.3). At 10%, every 7.2 years. This rule works because of the exponential nature of compounding.
Why regular contributions matter so much
Adding even a small regular contribution dramatically changes the outcome. Compare starting with $10,000 at 7% p.a. for 20 years:
| Monthly contribution | Final balance | Interest earned |
|---|---|---|
| $0/month | $38,697 | $28,697 |
| $100/month | $64,568 | $40,568 |
| $200/month | $90,440 | $52,440 |
| $500/month | $167,900 | $87,900 |
Frequently asked questions
| Year | Balance | Interest |
|---|---|---|
| Yr 1 | $13,201 | +$801 |
| Yr 2 | $16,634 | +$1,033 |
| Yr 3 | $20,315 | +$1,281 |
| Yr 4 | $24,262 | +$1,547 |
| Yr 5 | $28,495 | +$1,832 |
| Yr 6 | $33,033 | +$2,138 |
| Yr 7 | $37,900 | +$2,466 |
| Yr 8 | $43,118 | +$2,818 |
| Yr 9 | $48,714 | +$3,196 |
| Yr 10 | $54,714 | +$3,600 |