Purchasing power — what inflation and Box 3 do to cash
A savings account never falls, which is why it feels safe. In real terms it falls whenever the rate it pays is below inflation, and it has paid less than inflation for most of the last fifteen years. This page converts both a deposit and an invested portfolio into today's euros so the comparison is made in the only unit that matters — what the money will actually buy.
The calculator
How it works
Both balances are compounded annually at their own rate, then divided by the compounded inflation rate to express them in today's money. Box 3 is charged each year on the balance at the start of the year, and only on the part above the tax-free threshold — currently €59,357 for one person. On that excess it taxes a deemed return rather than a realised one: 6.00% for investments and 1.28% for savings, at 36%, so the annual charge is 2.16% of the invested excess and 0.46% of the savings excess, whatever either actually earned. The break-even return is the one at which the invested balance just keeps its purchasing power over the horizon after that charge. The rates resolve from the same rules file the Box 3 simulator uses, so this page cannot drift away from it.
What it assumes
Each scenario is taxed as if it were your only Box 3 asset, with one person's threshold — a fiscal partner doubles it — and the 2026 rates are held for every year of the horizon, though they are reset annually. Inflation, the deposit rate and the expected return are each a single fixed number held for the whole horizon, and no fund cost or trading cost is applied.
Common questions
- Why is the break-even return higher than inflation?
- Because in the Netherlands the portfolio is charged every year whether or not it grew. Standing still therefore requires covering inflation and the annual charge together, not inflation alone. That is a structural difference from a country that taxes only realised gains, where a flat year costs nothing, and it is why the break-even line on this page sits noticeably above the inflation slider.
- Does a deposit ever beat inflation?
- Sometimes, briefly, and not by enough to matter over a long horizon. Deposit rates follow short-term policy rates, which move with inflation but generally lag it, so the periods of positive real return tend to be short and are frequently followed by longer negative ones. Dutch consumer inflation averaged roughly two and a half percent a year from 2000 to 2024 and reached ten percent in 2022, which no deposit rate came close to matching.
- Is the deemed return the same as the tax rate?
- No, and conflating the two is the most common Box 3 mistake. The deemed rate is what the system assumes your assets earned; the tax rate is what it charges on that assumed amount. The annual cost is the product of the two, which is a much smaller number than either — and it applies to the value of the holding, so a year in which the portfolio fell still produces a bill.