Compound Interest Calculator
Most compound calculators quietly assume you keep every cent of the growth. This one charges the tax you would actually pay in Germany, the Netherlands or Ireland — every year, the way the tax office does.
Savings projection
How it builds up
| Point | Paid in | Balance | Tax so far |
|---|
Tax parameters verified September 2026: Germany 25% + 5.5% Soli = 26.375% with a €1,000 Sparer-Pauschbetrag; Netherlands box 3 at 36% with a €59,357 allowance and deemed returns of 1.28% (savings, provisional) and 6.00% (investments); Ireland DIRT 33% and 41% fund exit tax with eight-year deemed disposal. Single person, no partner allowance pooling.
Savings tax across the three
| Country | Rate | Charged on |
|---|---|---|
| Germany | 26.375% | Real gains over €1,000 |
| Netherlands | 36% | Deemed return on capital |
| Ireland | 33 / 41% | Interest / fund gains |
Same portfolio, same return — three very different outcomes after twenty years.
Where does the money come from?
Work out your net monthly pay first, then decide what you can realistically put aside.
Open Salary Calculator →Tax drag is the part nobody models
A 6% return taxed at 26% is not a 6% return minus a one-off haircut at the end. The tax comes out every year, so the money that would have compounded is gone permanently. Over twenty years that gap compounds too — and it is usually larger than the difference between a good fund and a mediocre one.
- Germany taxes what you actually earned, with a small annual exemption. Predictable, and mild at low balances.
- The Netherlands taxes what the law assumes you earned. In a bad year you pay anyway; in a great year the excess escapes. It is the only one of the three where you can owe tax on a loss.
- Ireland has the harshest treatment of funds in the group: 41%, with a forced tax event every eight years that breaks the compounding even for buy-and-hold investors.
Sources: Belastingdienst box 3 calculation page for 2026; German Abgeltungsteuer and Sparer-Pauschbetrag rules; Irish Revenue DIRT and investment undertaking exit tax. This is general information, not investment advice.
Frequently asked questions
How is compound interest calculated with monthly contributions?
Each month the balance grows by one twelfth of the annual return, then the new contribution is added. Because every month's growth is earned on the previous month's total, money paid in early does far more work than money paid in late.
How much tax do I pay on savings in Germany?
Investment income is taxed at a flat 25% Abgeltungsteuer plus a 5.5% solidarity surcharge on the tax itself — an effective 26.375%. The first €1,000 of gains per year is exempt under the Sparer-Pauschbetrag for a single person.
How does Dutch box 3 tax work in 2026?
Box 3 taxes a deemed return rather than your actual one. In 2026 the rate is 36%, the tax-free capital allowance is €59,357 per person, and the deemed return is 1.28% on bank savings (still provisional) and 6.00% on investments. If your real return is lower than the deemed rate, you still pay.
Why does my Irish fund balance drop every eight years?
Irish funds and most ETFs face a deemed disposal: every eight years you are taxed at 41% on the accumulated gain even if you sell nothing. The tax leaves the account, so the balance compounds from a lower base afterwards.