Investing
Compound interest calculator
Project how a starting balance plus regular contributions grow when interest compounds monthly, and see how much of the result is your money versus interest.
The numbers here are examples. Interest rates, tax bands and every result are sample starting points or values you type in yourself. Nothing is pulled from a live rate feed or a bank, and the results are estimates only. Always check real figures with your bank, lender or a qualified adviser before making a decision.
Your plan
Projected value
Balance after 20 years
9% return, compounded monthly
You contributed
$163,717
Interest earned
$249,590
Contributions vs. growth
Growth curve
Compound interest calculator
Balance after 20 years
$413,306
- Total contributions
- $163,717
- Interest earned
- $249,590
- Monthly contribution
- $400
- Assumed return
- 9%
How the answer is worked out
Each month the balance grows by the monthly rate and then the contribution is added:
balance = balance × (1 + r) + contribution
where r is the annual rate ÷ 12 ÷ 100. After twelve months the contribution is increased by the step-up percentage, if any. Total contributions is everything you paid in (including the opening balance); interest earned is the final balance minus that.
Frequently asked questions
Monthly. The annual rate is divided by twelve and applied to the balance each month, then the month's contribution is added.