Box 3 covers income from savings and investments — what most other countries would simply call a wealth tax. For an expat with modest savings the sums are small. For anyone with a substantial portfolio, a second property, or significant assets held abroad, Box 3 can quietly become the largest line on a Dutch tax bill.
It is also the most legally unstable part of the Dutch tax system. The regime has been under sustained court challenge for a decade, the rules in force for 2026 are an interim patch, and a replacement has already slipped its deadline more than once. Understanding both the current mechanics and the direction of travel matters if you are making decisions with a multi-year horizon.
Why the system works the way it does
Until 2017 Box 3 assumed a flat deemed return — typically 4% — on your total assets and taxed that assumption at 30%. Your actual return was irrelevant. Someone holding cash earning almost nothing through the zero-interest years was taxed as though they had earned 4%.
In December 2021 the Hoge Raad, the Dutch Supreme Court, ruled that this breached the European Convention on Human Rights' protection of property, because it taxed gains that did not exist. The government had to abandon the old model, and what replaced it — in force since 2023 and recalibrated annually — is a compromise: still deemed returns, but differentiated by asset type so the assumptions sit closer to reality.
How 2026 actually works
Assets are sorted into three categories, each with its own deemed return: bank deposits at roughly 1.44%, other investments — shares, bonds, investment property, crypto — at roughly 6.04%, and debts at roughly 2.62%, which is subtracted. These percentages are recalculated each year against market averages.
The resulting deemed return is taxed at a flat 36%. Before that, a tax-free allowance (heffingsvrij vermogen) of €57,684 per person applies in 2026 — €115,368 for fiscal partners filing together. Below the allowance, nothing is owed.
The category split matters enormously. Cash is taxed as though it earned 1.44%; anything classed as an investment is taxed as though it earned 6.04%, whether or not it did. In a bad market year you can owe meaningful tax on a portfolio that lost value — which is precisely the objection that keeps returning to court.
A worked example
A single expat holds €40,000 in savings and €100,000 in shares at the start of the year, with no relevant debts. Total assets €140,000, less the €57,684 allowance, leaves a taxable basis of €82,316.
The deemed returns compute separately: €40,000 × 1.44% = €576, and €100,000 × 6.04% = €6,040, totalling €6,616. The allowance is then applied proportionally — roughly 41% of the assets sit below it, so roughly 41% of the deemed return is exempt. That leaves approximately €3,910 taxable, and at 36% the bill is approximately €1,408.
Note what drove that figure: the €100,000 in shares generated over 90% of the deemed return. If the same €140,000 were entirely in cash, the tax would be a small fraction of it.
The valuation date, and why January matters
Box 3 is assessed on a snapshot: the value of your assets on 1 January of the tax year. Not an average, not a year-end figure — a single day.
This has a consequence worth planning around. Assets held on 1 January are taxed for that year; a large purchase made on 2 January sits outside the calculation until the following year. Equally, a big bonus landing in your account in late December is caught, where the same payment a fortnight later would not have been. This is legitimate timing awareness rather than avoidance, and it is the single most useful practical fact about Box 3.
Counter-proof: when your actual return was lower
Following the litigation, arrangements have existed allowing taxpayers whose actual return was lower than the deemed return to have the lower figure applied instead. This matters most in a year when markets fell, or when a portfolio classed as "investments" at 6.04% in fact returned far less.
The mechanism, the years it covers, and the evidence required have shifted as the legislation and the case law have developed, and further rulings continue to reshape it. If you had a materially bad year on assets that Box 3 assumed did well, this is worth raising specifically with a Dutch tax adviser — the amounts involved can be substantial and the position is not something to determine from a general guide.
What counts, and what does not
In Box 3: bank and savings balances, investment accounts holding shares, ETFs, bonds and funds, cryptocurrency, second homes and investment property, loans you have made to others, and life insurance policies with a savings component.
Not in Box 3: your primary residence, which sits in Box 1 along with its mortgage; substantial company holdings of 5% or more, which sit in Box 2; ordinary household possessions; art and collectibles held for personal enjoyment rather than investment; and pension assets meeting Dutch pension rules.
Two edge cases catch expats regularly. Foreign property is reportable even though a double-taxation treaty may mean the Netherlands ultimately does not tax it — the reporting obligation and the taxing right are different questions, and failing to report because you assumed it was exempt is a filing failure. Foreign pensions vary: whether a foreign scheme is recognised as a pension or treated as an ordinary investment depends on its structure, and getting this wrong in either direction is common.
Reporting, and why foreign assets now surface
Box 3 assets go on your annual return at their 1 January value. Dutch banks report balances directly to the Belastingdienst, so domestic accounts arrive pre-filled. Foreign accounts and investments you must declare yourself.
The important change is that not declaring them is no longer a practical option. Under the Common Reporting Standard the Belastingdienst receives account data automatically from tax authorities across most of the world. Assets that once went unnoticed now routinely appear, and a mismatch between what you declared and what a foreign authority reported is precisely the kind of discrepancy that triggers an enquiry. Our tax filing guide covers the return itself.
The 30% ruling and foreign assets
Holders of the 30% ruling have historically been able to elect treatment as a partial non-resident taxpayer, which excludes foreign-held Box 3 assets from the Dutch calculation entirely. For someone with a large portfolio held abroad, this election has been worth considerably more than the salary allowance the ruling is known for.
This is an area that has been subject to legislative change and transitional arrangements in recent years. Confirm its current availability and how it applies to your circumstances with a Dutch tax adviser before relying on it — do not assume it remains available simply because it was in a previous year, and do not plan a move around it without checking.
Fiscal partners: the allocation is a choice
If you have a fiscal partner, your combined Box 3 assets can be allocated between you however you choose on the return. Because each partner has their own tax-free allowance, using both allowances fully is the baseline optimisation, and couples who default to whatever the return suggests frequently leave money unclaimed. It costs nothing to test more than one split and compare the combined result.
Where this is heading
The government has committed to replacing the deemed-return system with one based on actual realised returns — interest, dividends, and realised capital gains. The target was 2027, then 2028, and the timetable has slipped repeatedly.
For most savers a realised-return system would be gentler than the current assumptions. For active investors it would be more administratively demanding, requiring genuine tracking of gains rather than a single January snapshot. Until it arrives, plan on the interim rules applying — and treat any specific future date you read as provisional.