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Total contributed
Compound Interest Calculator with Monthly Deposits
Compound interest rewards time and consistency. This calculator projects the future value of an initial sum that grows at a stated annual rate, with optional monthly deposits added along the way. It is useful for retirement accounts, emergency funds and any long-term savings goal where you want a clear picture of how rate, time and contributions interact.
Interest is applied using the selected compounding frequency. Additional contributions are added at the end of each month.
Please enter valid, non-negative values.
Final balance
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Interest earned
How to Use the Compound Interest Calculator
- Enter the starting balance and expected annual interest rate.
- Set the time horizon in years.
- Add a regular monthly contribution if you will deposit ongoing money.
- Review final balance, total contributions and interest earned.
Enter your starting amount, the expected yearly rate and the number of years. Choose how often interest compounds: monthly, quarterly, annually or daily. Add a monthly contribution if you plan to keep saving, or leave it empty to see growth on the starting amount alone. The results show the final balance, the total you paid in and the interest earned.
Compound Interest Calculator Formula Explained
Future Value of a Growing Annuity + Compound Principal
Future value of the initial principal is P(1 + r/n)^(nt), where r is the annual rate, n compounds per year and t is years. Future value of regular deposits A is A × [((1 + r/n)^(nt) − 1) ÷ (r/n)]. The two results are added for the total. Monthly deposits with monthly compounding are the most common retail case. Small differences in rate or extra years of compounding produce large gaps in the final number.
The calculator works month by month. Each month it adds that month’s interest, then adds your deposit at the end of the month. For monthly compounding the monthly growth factor is 1 + rate ÷ 12. For other frequencies it uses the equivalent monthly factor, (1 + rate ÷ frequency)^(frequency ÷ 12). For monthly compounding the result matches the closed-form formula above. Taxes, fees and rate changes are not included. Treat it as an estimate for planning, not as financial advice.
Compound Interest Calculator Example Calculation
Worked example: start with €10,000 at 4% a year, compounded monthly, for 15 years, with €100 added each month. The final balance is €42,812.07. You paid in €28,000.00 (10,000 + 100 × 180), so €14,812.07 is interest. Interest compounds on both the starting balance and every deposit. Without the monthly deposits, the same €10,000 grows to only €18,203.02, about 43% of the final balance above.
When to use this tool
Use this for long-term savings goals, emergency-fund projections, or comparing compound growth assumptions across accounts and investment plans.
Key Features & Benefits of This Compound Interest Calculator
- Monthly contributions included — models regular deposits on top of your starting balance, not just a single lump sum.
- Instant, free and private — runs entirely in your browser with no sign-up and no data sent anywhere.
- Clear breakdown — separates total contributions from interest earned so you can see exactly how much growth compounding added.
- Currency-agnostic — enter amounts in euros, dollars, or any currency; the maths works the same either way.
Good to know
Inflation reduces real purchasing power of a nominal balance. For long horizons, consider comparing results with a conservative real return assumption as well as the headline rate.
Compound Interest Calculator — FAQs
Does this account for taxes or fees?
No. The projection is pre-tax and assumes the stated rate is earned net of fees. Real account returns may differ.
What rate should I use?
Use a conservative long-term expected return for the asset class you hold, not last year’s peak performance.
Why does starting early matter so much?
Early contributions experience more compounding periods. A smaller sum invested longer often overtakes a larger sum invested later.
How often should interest compound for the best result?
More frequent compounding (monthly vs. annually) produces slightly higher returns at the same stated annual rate, because interest starts earning interest sooner. The difference is usually small compared to the rate itself or the size of your contributions.
Sources and review
Sources last checked: . These sources give the background for this calculator. They are general information, not financial advice.
- MoneyHelper: Interest rates explained: what compound interest is, and that the interest you earn can change if rates change.
- CFPB: How does compound interest work?: a worked example you can compare with the figures from this calculator.