Compound interest calculator
Project your savings growth, measure the impact of recurring deposits and see what time could do for your money.
Your projection
Simulate your capital
Adjust every assumption. Your results and chart update instantly.
Your balance over time
Ending balance breakdown
Effective annual rate: 5 %Indicative projection with a constant return, before tax and fees.
Understand the calculation
How does compound interest work?
Compound interest is added to your balance and earns further interest. The formula shows how an initial amount grows without additional deposits.
Understand the numbers
How much could saving €200 a month grow to?
Time changes both how much you contribute and how long each deposit can earn a return. These three projections use the same monthly contribution.
| Duration | Total contributed | Estimated ending balance | Estimated gains |
|---|---|---|---|
| 10 years | €24,000 | €30,873 | €6,873 |
| 20 years | €48,000 | €81,161 | €33,161 |
| 30 years | €72,000 | €163,075 | €91,075 |
Assumptions: no initial balance, €200 deposited at each month-end, a constant 5% annual rate and annual compounding. The calculator uses the equivalent monthly rate. Amounts are rounded to the nearest euro, before fees, tax and inflation. These are illustrative scenarios, not guaranteed returns.
How do you calculate compound interest with monthly deposits?
Each deposit joins the balance and starts earning interest. A deposit made early has more time to grow than one made near the end. The ending balance combines the growth of your initial amount with the growth of each deposit.
For equal deposits made at each month-end, the formula is:
C = C₀ × (1 + i)ᴺ + V × ((1 + i)ᴺ − 1) / i
C₀ is the initial balance, V the monthly deposit, N the number of months and i the equivalent monthly rate. With annual compounding at 5%, i = (1 + 0.05)^(1/12) − 1, or about 0.4074% per month. At a zero rate, the ending balance is simply C₀ + V × N.
Starting from zero with €200 deposited at each month-end, the balance is €200 after the first month. In month two, that €200 earns about €0.81 before the next deposit brings the balance to €400.81. The calculation repeats each month.
A deposit at the beginning of the month gets one extra month of growth. In the formula, the deposit term is then multiplied by (1 + i). Use the deposit timing option to compare the two cases.
Simple vs compound interest: what is the difference in euros?
Simple interest is earned only on the initial amount. Compare both methods for €10,000 over 20 years at 5% a year, with no additional deposits.
- Initial balance
- €10,000
- With simple interest
- €20,000
- With compound interest
- €26,533
Simple interest: 10,000 × (1 + 0.05 × 20). Compound interest with annual compounding: 10,000 × 1.05²⁰. The difference comes entirely from reinvesting interest in this constant scenario, before fees and tax.
How do the rate and duration affect the result?
The first table varies the duration. Here, the duration stays at 20 years and only the rate changes: you still deposit €200 at each month-end, contributing €48,000 in total, with no initial balance and annual compounding.
| Hypothetical annual rate | Total contributed | Estimated ending balance | Estimated gains |
|---|---|---|---|
| 0 % | €48,000 | €48,000 | €0 |
| 3 % | €48,000 | €65,371 | €17,371 |
| 5 % | €48,000 | €81,161 | €33,161 |
These rates illustrate the sensitivity of the calculation; they do not predict investment performance. Constant returns simplify reality: returns can vary and capital can fall. Amounts exclude fees, tax and inflation.
FAQ
Frequently asked questions
The essentials to know before interpreting your projection.
Can I start with no initial savings?
Yes. Enter €0 as the initial amount and choose a recurring deposit. Each deposit starts earning interest according to the timing selected. With neither an initial amount nor deposits, the balance stays at zero.
What happens if I stop making deposits?
The accumulated balance continues to change with the investment return. First simulate the period up to your last deposit. Then use that ending balance as the initial amount in a second simulation with recurring deposits set to zero. Actual returns can vary and capital can fall.
How do I calculate compound interest in Excel?
For €200 deposited at each month-end over 20 years, starting from zero at 5% a year with annual compounding, use =FV((1+5%)^(1/12)-1,20*12,-200,0,0). The monthly rate is equivalent to the 5% annual rate. Deposits are negative so that the ending balance is positive. The result is about €81,161 before fees and tax. Argument separators can depend on your regional settings.
What return rate should I use?
Use a cautious assumption suited to your savings plan. Historical performance never guarantees future returns, so compare several scenarios instead of relying on one rate.
Are taxes and fees included?
No. Results are before tax and fees. You can lower the annual rate to approximate their impact.
Why account for inflation?
Inflation reduces future purchasing power. Real value shows what the ending balance could represent in today's money.