Compound Interest Calculator
Last verified · Methodology
Estimate how your savings or investments could grow with compounding and recurring monthly contributions.
Why starting early matters more than the amount
Compound interest rewards time above everything else. Someone who invests $200/month from age 25 to 35 and then stops will end up with more at 65 than someone who invests $200/month from 35 to 65. Ten years of head start beats 30 years of contributions.
Here is a concrete example at 7% annual return, compounded monthly:
| Monthly contribution | Starting age | Years invested | Value at 65 |
|---|---|---|---|
| $200 | 25 | 40 years | $524,000 |
| $200 | 35 | 30 years | $243,000 |
| $400 | 35 | 30 years | $486,000 |
The 35-year-old has to double their monthly contribution just to match what the 25-year-old built with half the investment.
| Rate | 10 years | 20 years | 30 years |
|---|---|---|---|
| 4% | $14,802 | $21,911 | $32,434 |
| 5% | $16,289 | $26,533 | $43,219 |
| 6% | $17,908 | $32,071 | $57,435 |
| 7% | $19,672 | $38,697 | $76,123 |
| 8% | $21,589 | $46,610 | $100,627 |
| 10% | $25,937 | $67,275 | $174,494 |
A compound interest calculator estimates how money can grow over time when returns are added back into your balance. It helps you model an initial deposit, recurring contributions, and an expected annual return.
Contributions are the dollars you personally add, such as your starting balance and monthly savings. Interest earned is the estimated growth generated by compounding on top of those contributions.
Many savings and investment examples use monthly compounding, but some accounts may compound daily, quarterly, or annually. This calculator lets you compare those scenarios to see how frequency changes the estimate.
No. This tool is for planning and education only. Actual investment returns can rise or fall and may differ significantly from any fixed-rate projection.
Yes. Your inputs stay in your browser for calculation purposes. If site analytics are enabled, they only measure anonymous product usage and never include the numbers you enter.
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