Savings Calculator: Which Monthly Amount Reaches Your Goal

Which monthly amount reaches your goal

The question behind every savings plan: how much do I need to put aside each month to end up with a specific sum? The answer depends on three things: the duration, the interest rate, and whether you start with any capital. For a goal of €100,000 in 20 years with no starting capital, the calculator returns:

Between 2.5% and 7% lies a gap of almost €126 a month for the same goal. At 7%, more than half of the target comes from interest; at 2.5%, less than a quarter. In reverse, with the rate fixed at €250 a month, “Duration” mode shows how long the road to €100,000 is: 24 years and 4 months at 2.5%, 19 years and 10 months at 5%, and 17 years and 5 months at 7%.

The third row shows what duration does. At 7%, €90,000 of your own deposits turns into €294,016.21. The interest of €204,016.21 is more than double what you paid in yourself. How this compound interest effect grows with time shows in the comparison of the first and third rows: at 7%, the third decade adds more final capital than the first two combined.

Which interest rate is realistic

The calculator starts at 2.5%. That is a placeholder, not a forecast. Where an investment actually lands depends on what sits behind the savings plan:

• Savings and fixed-term deposits. The ceiling for what a bank can pay on a permanent basis is the rate at which it parks its own money with the European Central Bank: the deposit facility rate of 2.25% (since 17 June 2026). More than that for a bank savings plan means assuming a promotional offer, not a standing condition.
• Equity ETFs. The European securities regulator ESMA reports a net return of 10.1% per year for equity ETFs in the EU market over 2020 to 2024, or 6.0% in real terms after ongoing costs and inflation. Actively managed equity funds returned 7.5% nominal and 3.6% real over the same period. Five years is a short and unusually good stretch, though.
• The long view. The German Equity Institute (Deutsches Aktieninstitut) gives a reading example in its DAX return triangle: someone who bought DAX shares at the end of 1996 and held them until the end of 2013 saw the portfolio grow by an average of 7.3 percent per year. That is a return including dividends, before costs and tax, and the institute adds that past data is no reliable indicator of future performance.

For equity investments, 5 to 7% is a defensible assumption; for bank products, the ECB rate is the yardstick. In both cases, net out inflation: at 5% interest and 2% inflation, the real return is not 3% but 1.05 ÷ 1.02 − 1 = 2.94%. The calculator knows nothing about inflation; to see the real value, enter the real rate.

The five calculation modes

The switch above the calculator sets which value is unknown. You enter the other four:

• Final capital: initial capital, savings rate, duration and interest rate are known. The calculator shows the final capital, the sum of deposits and the interest earned. This is the default.
• Initial capital: you know the final capital you want and the rate you can afford. The result is the lump sum needed at the start. If the rate alone is enough, the value can turn negative.
• Savings rate: the path of the first table. The result is the rate per savings interval, rounded to the cent.
• Interest rate: which return takes initial capital and savings rate to the desired final capital? Shown with two decimals.
• Duration: how long until the goal? The result appears in years and months, for instance “19 Years and 10 Months”.

All euro amounts are shown to the cent. The savings interval can be set to yearly, half-yearly, quarterly or monthly; the savings rate then applies per interval, not per month.

In advance or in arrears, and what the interval does

“In advance” means the payment arrives at the start of the interval and earns interest immediately. “In arrears” means it arrives at the end, and interest starts one interval later. With €250 a month over 20 years at 5%, in advance gives €101,864.45 and in arrears gives €101,451.12. The difference of €413.33 is exactly one month of interest on every single payment. A savings plan executed on the first of the month is paid in advance.

The savings interval works differently from what many expect. The calculator converts the annual rate into an equivalent rate per interval, so 5% per year stays 5% per year whether interest is credited monthly or yearly. What changes is when the money starts working. The same €3,000 a year gives, over 20 years at 5%:

Paying the full annual amount on 1 January ends highest, because all of the money works all year; the monthly saver sits in between. The interval is a question of cash flow, not of return.

Compounding or simple interest

“Compounding” in the calculator means every interest credit is added to the capital and earns interest itself from then on. “Simple interest” means the interest is paid out and stops working; the calculator still adds it to the final capital at the end, as if it were sitting next to the plan uninvested. With €250 a month, 20 years and 5%, compounding gives €101,864.45 and simple interest gives €90,125.00. The €11,739.45 difference is compound interest: interest earned on earlier interest.

Tax: what the exemption order does

Investors resident in Germany pay 25% flat-rate capital gains tax (Abgeltungsteuer) on investment income, 26.375% including the solidarity surcharge, and 27.8186% or 27.9951% with church tax. How these rates come together is explained with the capital gains tax calculator. The saver’s allowance (Sparer-Pauschbetrag) of €1,000 per person and year stays tax-free, double that for jointly assessed spouses. It only takes effect through an exemption order (Freistellungsauftrag) filed with your bank; without one, the bank withholds the tax and you reclaim it through your tax return.

In the calculator, switch tax on under “Tax capital gains”. It then works like this: at the end of each year, the year’s interest is added up. If it exceeds the allowance you entered, the excess is taxed at the rate you entered and the tax is deducted from the capital. The allowance is available afresh every year.

In the early years, therefore, no tax falls due at all. With €250 a month at 5%, annual interest only exceeds €1,000 in year seven (€1,128.36). Over 20 years the picture is:

Tax costs more than the amount deducted: it also costs the interest that money can no longer earn. Over 30 years, €30,089.16 is missing at the end, although only €20,645.41 of tax was paid.

What the calculator does not model

The interest rate is constant over the entire duration. Real equity returns fluctuate, and a bad decade at the start weighs differently from one at the end; the calculator shows the average path, not the range. It does not know costs: ongoing fund charges, order fees and spreads reduce the return, so the rate you enter should be a net figure after costs. The savings rate stays the same throughout; an annual increase or a pause cannot be entered. And the rate is nominal: to know what the final capital is worth in today’s purchasing power, use the real rate.

Sources

• European Central Bank: Key ECB interest rates (deposit facility 2.25% since 17 June 2026) – accessed 2 September 2026
• Deutsches Aktieninstitut: DAX-Rendite-Dreieck (DAX return triangle, in German), edition of 20 January 2026, data as of 31 December 2025 (reading example 7.3%, methodology notes) – accessed 2 September 2026
• ESMA: Market Report on Costs and Performance of EU Retail Investment Products, March 2026, data as of 2024 (2020–2024 returns of equity ETFs and active equity funds) – accessed 2 September 2026
• German Income Tax Act: Section 32d EStG (tax rate 25%) and Section 20 EStG (saver’s allowance), in German – accessed 2 September 2026
• German Investment Tax Act: Section 20 InvStG (30% partial exemption for equity funds), in German – accessed 2 September 2026

Frequently asked questions about the savings calculator