Belgium's capital-gains tax: sell at once, or spread it out?

Since 1 January 2026, Belgium taxes realised gains on financial assets — shares, funds, ETFs — at 10%, with an exemption of €10,000 per person per year. So the question is no longer just "when to sell?" but "how to sell?": the same portfolio can produce a very different tax bill depending on whether you sell everything at once or spread the sale over several years.

How the tax works

10% on the realised gain — as long as you don't sell, nothing is due.
€10,000 of exemption per year, per person. Only the part of the gain above that amount is taxed.
Unused exemption carries forward: each year without a sale raises it by €1,000, up to a cap of €15,000.
Couples get one each: two exemptions, so up to €20,000 of gains exempt in the same year on a joint portfolio.
What counts is the gain, not the amount sold: selling €50,000 of shares bought for €40,000 = €10,000 of gain.

A worked example

A portfolio of €60,000 with 30% unrealised gains — €18,000 of gain not yet realised.

Sell everything in 2027: €18,000 of gain, minus the €10,000 exemption → €8,000 taxable × 10% = €800 in tax.

Spread over 2027 and 2028: two sales of €9,000 of gain each, each year under the exemption → €0 in tax.

Same portfolio, same amount sold: an €800 difference, purely from the calendar.

What this example doesn't tell you

The example above is too simple to decide on — and that's precisely the problem:

Your numbers aren't these. Your real unrealised gain depends on your purchase prices, and that's what determines whether spreading saves you €0, €800 or €3,000.
Waiting has a cost and a return. While you spread, the portfolio keeps moving — the next tranche's gain grows with the market. Spreading isn't always the winner.
The tax is only one line of your situation. What matters is the effect on your trajectory: your net worth at pension age, the age at which you could stop working. A tax decision is judged over years, not on one bill.

This is a simulation problem, not a back-of-the-envelope one: several years, two pots of money, market uncertainty. That's exactly what Percol does — it applies the rules above to your numbers and compares your options side by side, across 1,000 simulated futures.

Sources and limits

Rules as in force on the date shown at the bottom of this page, checked against the texts published in the Belgian Official Gazette (Moniteur belge / Belgisch Staatsblad). The simulator assumes an aggregate position (detailed lots arrive in v1.5), an unindexed exemption — a prudent assumption — and a sale followed by immediate rebuying: only the tax leaves the portfolio. Percol produces simulations, not investment or tax advice.