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Reinvestment
Returns remain invested, so the next period starts from a larger capital base.
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Capital growth
Capital growth
Compound interest calculator
Estimate how capital may grow when returns are reinvested and new contributions are added. Change the amount, expected return and time horizon to update the result instantly.
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Quick calculation
Estimate the future value of your investments
The estimate assumes monthly compounding and contributions at the end of each month. It is a model, not a market forecast.
Estimated value111,651 $
Your contributions70,000 $
Growth from returns41,651 $
How compounding works
Returns can start generating additional returns
With simple interest, growth is calculated only on the original amount. With compound interest, accumulated gains stay invested and become part of the base for future periods.
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Time matters
The longer the horizon, the more visible repeated compounding can become.
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Recurring contributions
New contributions increase the capital base and can participate in future growth as well.
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Returns are not guaranteed
A fixed rate in a calculator is a scenario assumption. Real market returns vary.
Formula
What drives the final value
For monthly calculations, the model uses FV = P × (1 + i)^n + PMT × ((1 + i)^n − 1) / i, where i = (1 + r)^(1/12) − 1. Contributions are assumed to be made at the end of each month.
P — starting capital
PMT — monthly contribution
r — effective annual return
i — equivalent monthly return
n — number of months
Example
A longer horizon can change the outcome
Starting with $10,000 and adding $500 at the end of each month at an 8% effective annual return gives $70,000 in total contributions after 10 years, an estimated value of about $111,651, and about $41,651 of growth above contributions.
Taxes, fees, inflation and market volatility can materially change the actual result.
Starting capital10 000 $
Monthly contribution500 $
Annual return, %8%
Years10
Your contributions70 000 $
Estimated value111 651 $
Growth from returns41 651 $
Simple vs compound interest
The key difference is what happens to the return you earn
Simple interest
Growth is calculated only on the original principal. Earned interest does not increase the base for the next calculation.
Compound interest
Returns are added to capital and can themselves generate future returns. The effect becomes more visible over longer periods.
Keep in mind
Markets do not grow at one fixed rate every year. This calculator is useful for comparing scenarios, not predicting future returns.
Questions
Common questions about compound interest
What is compound interest in simple terms?
It means previously earned returns stay invested and can generate additional returns later.
Why does time matter so much?
Because each new period can build on a base that already includes previous growth. More periods mean more repetitions of that effect.
Can I include monthly contributions?
Yes. The quick calculator on this page includes monthly contributions, and the main calculator supports more detailed scenarios.
What return should I enter?
Compare several assumptions — conservative, base and optimistic. Historical returns do not guarantee future results.
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