Compound Interest Calculator
See how your wealth grows over the years with compound interest and a monthly contribution.
- Contributions
- €46,000.00
- Interest earned
- €28,594.83
| Year | Balance |
|---|---|
| 1 | €12,967 |
| 2 | €16,087 |
| 3 | €19,365 |
| 4 | €22,812 |
| 5 | €26,435 |
| 6 | €30,243 |
| 7 | €34,246 |
| 8 | €38,454 |
| 9 | €42,877 |
| 10 | €47,527 |
| 11 | €52,414 |
| 12 | €57,551 |
| 13 | €62,951 |
| 14 | €68,628 |
| 15 | €74,595 |
Capital growth over 15 years
Show details table
| Year | Contributions | Interest | Balance |
|---|---|---|---|
| 1 | €12,400.00 | €567.39 | €12,967.39 |
| 2 | €14,800.00 | €1,286.60 | €16,086.60 |
| 3 | €17,200.00 | €2,165.39 | €19,365.39 |
| 4 | €19,600.00 | €3,211.93 | €22,811.93 |
| 5 | €22,000.00 | €4,434.80 | €26,434.80 |
| 6 | €24,400.00 | €5,843.03 | €30,243.03 |
| 7 | €26,800.00 | €7,446.09 | €34,246.09 |
| 8 | €29,200.00 | €9,253.96 | €38,453.96 |
| 9 | €31,600.00 | €11,277.11 | €42,877.11 |
| 10 | €34,000.00 | €13,526.55 | €47,526.55 |
| 11 | €36,400.00 | €16,013.87 | €52,413.87 |
| 12 | €38,800.00 | €18,751.23 | €57,551.23 |
| 13 | €41,200.00 | €21,751.44 | €62,951.44 |
| 14 | €43,600.00 | €25,027.92 | €68,627.92 |
| 15 | €46,000.00 | €28,594.83 | €74,594.83 |
How your money grows with compound interest
Compound interest is one of the most powerful levers in long-term wealth building. Interest credited to your capital earns further interest in the following years. Over long periods this leads to exponential rather than linear growth.
This is exactly what the compound interest calculator makes visible: it separates your contributions from the interest earned and shows, year by year, how the interest portion contributes ever more strongly to growth over time.
The maths behind it
Classic compound interest is calculated with the formula final amount = initial capital × (1 + rate)^years. If a regular contribution is added, the calculator also sums each payment with its remaining compounding period – month by month rather than just once a year.
The three levers are the interest rate, the term and the contribution. The term has the strongest effect because it enters exponentially: starting earlier pays off disproportionately, even with small amounts.
Worked example: €10,000 over 20 years
Suppose you invest €10,000 once at 5% per year with annual compounding, and no further contributions. After 20 years this has grown to around €26,530 – more than 2.6 times the amount, even though you added nothing.
More than half of the increase arises in the second half of the term. That is the essence of compounding: it accelerates the longer the capital is working.
Common mistakes when estimating
In their heads most people significantly underestimate long-term growth because they think linearly rather than exponentially. Also watch real versus nominal values: a 5% return with 2% inflation corresponds to only about 3% real gain in purchasing power.
Keep in mind that the calculator shows interest before taxes and costs. For a view after (German) capital gains tax, use the savings interest calculator with its tax option.
Frequently asked questions
How does the compound interest calculator work?
Enter your initial capital, monthly contribution, annual interest rate and term. The calculator simulates the growth period by period and shows the final amount, total contributions and interest earned.
What is the compounding effect?
With compound interest, previously credited interest itself earns interest in later periods. As a result your capital grows exponentially – the longer the term, the stronger the effect.
Monthly or yearly interest crediting?
With monthly crediting, interest is calculated twelve times a year and reinvested, which slightly increases the final amount compared to yearly crediting.
What interest rate is realistic?
It depends on the type of investment: instant-access savings are usually in the low single digits, while broadly diversified equity ETFs historically returned around 6–8% before costs over the long run. Future returns are not guaranteed – be conservative and consider several scenarios.
How much does the term affect the result?
A great deal, because the term enters exponentially. Doubling the number of years leads to far more than a doubling of the final amount. Starting early is therefore more effective than paying in large amounts later.
Are taxes and inflation included?
No, the calculator shows nominal gross growth before taxes and inflation. For a net view use the savings interest calculator; for purchasing power, subtract expected inflation from the interest rate.