Compound interest with monthly contributions
Calculate how much your savings can grow by contributing a fixed amount every month, on top of an initial capital, at a given annual interest rate.
Results
Final capital
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Total contributed
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Interest generated
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The final capital is calculated compounding monthly: initial capital × (1 + r)^n, plus the future value of monthly contributions [(1+r)^n - 1] / r, where r is the monthly interest rate and n the number of months.
Year-by-year evolution
| Año | Saldo final | Aportado acumulado | Interés acumulado |
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When should you use this calculator?
This page is designed for anyone who saves or invests periodically every month (not just with a lump-sum initial capital) and wants to see the cumulative effect of those monthly contributions. The fields are pre-filled with a typical monthly contribution example; change any value to fit your own situation.
Practical example
With €1,000 of initial capital and a €100 monthly contribution at 5% annual interest over 10 years, the final capital is €17,175.24: of that amount, €13,000 comes from what was contributed (€1,000 initial plus €12,000 across 120 contributions of €100) and €4,175.24 is interest generated by compounding on those contributions.
Practical tips
Contributing an amount every month instead of only at the start smooths out the effect of price volatility if you invest in products whose price fluctuates (a strategy known as dollar-cost averaging), and turns saving into a regular habit that's usually easier to sustain over time than gathering a large lump sum before you start investing.
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Frequently asked questions
What's the difference between contributing only an initial capital and also contributing every month?
Contributing only an initial capital grows just that amount through compounding; also contributing every month adds to the final result both the interest earned on the initial capital and the interest earned on each of the monthly contributions, which noticeably speeds up total growth.
Can I change how much I contribute each month over time?
This calculator assumes a constant monthly contribution throughout the period. If your actual contribution varies over time, you can recalculate with different monthly contribution values to approximate different scenarios.
Does this calculator account for inflation?
No, it calculates the nominal growth of the capital. To see the effect of inflation on that future capital's purchasing power, you can use this site's inflation calculator.