Compound Interest Calculator
See how savings grow with compound interest. Enter an initial amount, monthly contribution, rate and term to get the final value, total gain and a yearly table.
Final value
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Total invested
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Total gain
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Term (months)
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Yearly breakdown
| Year | Contributed in year | Gain in year | Value at year end |
|---|
A monthly-compounded estimate. Taxes and fees are ignored and market risk is not reflected. Results are not guaranteed — this is not investment advice.
Done
Compound Interest Calculator
How to use
- 1
Enter amounts
Fill in the initial amount and the monthly contribution (either one alone works too).
- 2
Set rate and term
Choose an annual rate and the term (years plus extra months).
- 3
Review the growth
Check the final value, total gain and the year-by-year table of principal and value.
Features
- Compound simulation for an initial amount plus monthly contributions
- Instant final value, total invested and total gain
- Year-by-year table of contributions, gains and value
- Everything computed in your browser; nothing is transmitted
Use cases
Projecting recurring investments
Estimate the value of monthly contributions at an assumed rate in 10 or 20 years.
Saving for a down payment
Work out how term and monthly amount combine toward a target.
Education savings
Compare contribution plans against a school-enrollment deadline.
Details
Compound interest means earned gains are added back to the balance and keep earning. Both the initial amount and each monthly contribution grow at the monthly rate: the initial amount scales by (1 + r)^n, and the contributions grow by ((1 + r)^n − 1) ÷ r, where r is the monthly rate and n the number of months. Their sum is the final value.
This tool approximates monthly compounding by dividing the annual rate by 12 and rounds displayed amounts to whole currency units. Real investing involves taxes, fees, price fluctuations and rate changes, so use these numbers to understand the mechanics and sketch a plan — not as a promise of results. Nothing here is principal-guaranteed or investment advice.
Typical uses: estimating where recurring savings could end up, working backwards from a target to a monthly contribution, and seeing how strongly rate and duration affect the outcome. The yearly table shows the moment gains start exceeding contributions — the essence of compounding.
FAQ
What is compound interest?
It is the mechanism where earned gains are added back to the balance and start earning on their own. Compared to simple interest, growth accelerates the longer the term runs.
Does the result match real investment performance?
No. This is a monthly-compounded estimate that ignores taxes, fees, price fluctuations and rate changes. Real results vary with the market.
Can I calculate with a zero initial amount?
Yes. Either the initial amount or the monthly contribution alone is enough — only both being zero is an error.
Are the amounts I enter sent anywhere?
No. All computation happens locally in your browser and nothing you enter is transmitted.
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All processing happens in your browser. Your files are never uploaded.
Verified: Known cases, a 0% rate, error states and the yearly table are covered by browser tests
Did you know?
Under compounding, gains generate their own gains, so growth accelerates with time. By the rule of 72, at 3% a year the principal doubles in about 24 years.