Netherlands Box 3 Unrealised Gains Tax: Act Before 2028

A Netherlands Box 3 unrealised gains tax would tax paper gains before any sale. What international investors should review before 2028.

Most investors are comfortable with the idea of paying tax when they sell something at a profit. The unsettling part of the Dutch reform debate is the prospect of paying tax on gains you have not yet realised, on assets you still hold, simply because they rose in value over the year.

That is the essence of an unrealised gains tax, sometimes called an accrual or mark-to-market basis, and it has been a live feature of the discussion around how the Netherlands taxes private wealth under Box 3 from 2028. While the final design continues to be debated and legislated, the direction has prompted internationally mobile investors to ask a sensible question: what, if anything, should I do before the new regime takes effect?

This guide explains the concept, why it provokes such concern, and the measured steps worth reviewing now, without overreacting to rules that are not yet final as at 2026.

Realised versus unrealised: why the basis matters

Under a realisation basis, you are taxed when you dispose of an asset. Hold a portfolio that doubles over five years and sell nothing, and there is no charge in those years; the tax arises when you sell. This matches tax to actual cash and to a genuine, crystallised gain.

Under an accrual or unrealised basis, the annual increase in an asset's value is taxed in the year it occurs, whether or not you sell. A portfolio that rises 15 percent in a year generates a taxable amount even if you hold every position. The mirror image is also true: in a falling year, the system must decide how to relieve losses you have not actually crystallised.

The cash-flow consequence is the crux. Taxing unrealised gains can force investors to find cash, or even to sell assets, to pay tax on profits that exist only on paper and might reverse before they are ever realised. For illiquid holdings, the problem is acute.

Why the Netherlands ended up here

The Dutch Box 3 regime historically taxed a deemed return rather than actual income, and that approach was found wanting by the courts where the assumed return diverged sharply from reality. The reform programme aims to tax actual results instead.

The difficulty is that taxing actual results cleanly is easy for income such as interest, dividends and rent, but harder for capital growth. A pure realisation basis can defer tax for years and invites lock-in, where investors hold assets purely to postpone tax. An accrual basis captures growth as it happens but raises valuation, liquidity and fairness questions. The debate over which basis applies, and to which asset classes, is exactly why the final shape has moved and why specific mechanics should be treated as provisional.

Real estate is the sharpest example. Annual mark-to-market valuation of property is contentious and administratively heavy, so the treatment of property may differ from that of liquid securities. We would caution strongly against assuming a single uniform rule across all asset types.

There is also a constitutional dimension. The same property and equality protections that struck down the old deemed-return approach can, in principle, be invoked against features of a new regime that operate harshly. That tension is part of why the design has proven so difficult: lawmakers must produce something that both raises revenue predictably and survives challenge. For investors, the practical takeaway is humility about the final form, and a reluctance to bet heavily on any single proposed mechanic before it is law.

What an unrealised basis would change in practice

If an accrual element is adopted, three practical effects follow for investors with Dutch exposure.

Annual liquidity planning becomes essential. You may owe tax in years when you receive no cash from an asset. Holding some liquidity against that charge, rather than being fully invested in illiquid positions, becomes prudent.

Valuation discipline matters. Listed securities are easy to value; private company stakes, art, and certain property are not. An accrual regime requires defensible annual valuations, which is a real compliance cost and a potential dispute area.

Loss relief design is critical. A fair accrual system must allow relief when assets fall in value. How generously losses can be used, and whether they can be carried, materially affects the burden across a market cycle. This is one of the most important and least settled details.

Sensible steps to review before 2028

We frame these as a review, not a rush. Acting on unconfirmed rules can create its own problems.

Establish where each asset sits. Confirm which holdings fall in Box 3 as private investments, which sit in Box 2 as substantial shareholdings, and which relate to Dutch real estate. The reform affects these differently, and clarity here precedes any decision.

Reassess private versus structured holding. For some investors, holding assets through a company, fund or other vehicle may change the analysis once the new basis applies. Whether that helps depends on the final rules and on your wider, cross-border position, so it should be modelled rather than assumed.

Review residency timing thoughtfully. For those considering moving to or from the Netherlands, the timing of arrival or departure interacts with how and when gains are brought into charge. This is delicate and should be coordinated with home-country exit and entry rules.

Build liquidity awareness into the portfolio. If accrual taxation is adopted, a portfolio dominated by illiquid assets with no cash buffer is more exposed. This is a portfolio-construction point as much as a tax one.

Keep treaty relief in view. Where you are resident elsewhere but hold Dutch assets, or vice versa, treaties and foreign tax credits shape the final outcome. Domestic Dutch changes do not operate in isolation.

Document your cost base now. Whatever the final basis, clean records of acquisition cost, dates and improvements for each asset will make the transition far easier to handle and any future calculation more defensible. Good record-keeping is the one preparatory step that carries almost no downside regardless of how the rules land.

We have deliberately avoided quoting rates, thresholds or a definitive mechanic, because those are the elements most likely to shift before and shortly after 2028. The right posture is informed readiness, not premature restructuring around rules that may still change.

How HPT helps

We help internationally mobile clients understand how an accrual or realisation basis would touch their specific holdings, model private versus corporate and fund alternatives across the relevant jurisdictions, and time any residency or structural decisions so they are robust whatever final form the rules take. Where the prudent answer is to wait and prepare, we say so.

If Dutch wealth taxation is on your horizon, we would be glad to review your position before the 2028 regime takes hold.