What the exemption is
Belgium taxes realized capital gains on financial assets at a flat 10% for gains realized from 1 January 2026. Against that tax sits an annual exemption of €10,000 per taxpayer.
Two words in that sentence carry most of the weight.
Annual — the exemption belongs to a calendar year, and the tax year is the calendar year.
Per taxpayer — it belongs to the person, not to the account, not to the broker, and not to the instrument. Someone holding positions at four brokers still has one exemption of €10,000 in total, not four.
Why withholding at source does not deliver it
From June 2026, Belgian intermediaries withhold the 10% by default. That withholding happens on the transactions passing through that one intermediary.
An intermediary applying tax at source is working from a partial view. It knows what it settled itself. It does not know what was realized elsewhere in the same year, it does not know what losses were realized elsewhere, and it does not know how much of the €10,000 has already been consumed.
So the exemption cannot be applied at source. It is claimed only through the annual tax return — and the same is true of loss offsets. Tax withheld by a Belgian broker is therefore a provisional payment, not a final settlement.
The shape of the gap
Take a single Belgian broker withholding at source, and €9,000 of realized gains over the year.
- Withheld at source: €900 (10% of €9,000).
- Covered by the exemption: the full €9,000, since it sits under €10,000.
- Tax actually due on those gains: €0.
- Difference: €900, recoverable only via the return.
Nothing in that chain happens by itself. If the return does not carry the figures, the €900 stays where it is.
The picture gets wider with several brokers. Losses realized at one broker offset gains realized at another, but that offsetting also runs through the return, and — on the current reading, which is itself marked as needing verification in our source rules — only within the same year, with no carry-forward of losses into a later year. Verify that point with the FPS Finance or your accountant before relying on it.
Indexation and carry-forward: sources disagree
Two features of the exemption are not settled, and this article will not pretend otherwise.
Indexation. The €10,000 is described as indexed to inflation, so the figure applying to a given tax year may not be exactly €10,000. The current indexed amount is worth checking against the FPS Finance rather than assumed.
Carry-forward of unused exemption. Published sources disagree on the mechanism. Two readings circulate:
- an unused year accrues +€1,000 per year, up to a total exemption of €15,000, with the accrual resetting once a year fully uses its exemption;
- a running balance of unused exemption accumulates, again up to €15,000.
Those produce different numbers for the same investor. Until the mechanism is confirmed against the FPS Finance or a tax professional, any carry-forward figure — including one produced by Belfolio — is a working assumption rather than an answer. Belfolio treats it as a parameter precisely because it is expected to change.
What the return has to be able to show
To claim the exemption and any loss offsets, the return needs the realized result for the year across every broker, which in practice means, per disposal:
- the acquisition date, quantity and acquisition value of the parcel sold;
- for positions held before 2026, the 31 December 2025 value used as the acquisition value under the step-up rule;
- the disposal date, quantity and proceeds;
- the tax already withheld by each intermediary.
An export covering only the current year is usually not enough on its own: it contains disposals whose matching acquisitions sit in an earlier file.
Without a consolidated record it is not possible to demonstrate how much of the exemption was used, or how much withheld tax exceeds the tax finally due.
The capital gains tax simulator shows what the exemption does to a single sale; the calculator applies it across your full year.
Always verify your figures
Belfolio computes and presents these amounts for information only. This is not tax advice. Verify them with the FPS Finance or your accountant before filing.
Published 4 Jun 2026