Withholding or opt-out
Since June 2026 a Belgian intermediary withholds the capital-gains tax by default; opting out — or investing through a broker that does not withhold — moves the whole calculation to your own return. The amount is the same either way. This page shows what each route looks like for the year you expect.
Result
If it is withheld at source
- Taken during 2026
- €800.00
- Recoverable through the 2027 return
- €800.00
- Still due with the return
- €0.00
Withholding is taken per gain, as it is realized. It knows neither your annual exemption nor the losses that follow — both exist only on the return.
If you declare it yourself
- Taken during 2026
- €0.00
- To pay through the 2027 return
- €0.00
Nothing is settled during the year: you keep the records, add the year up across every account, and declare the total yourself. The exemption and loss offsets apply through that same return.
What becomes of the amount withheld
- Returned after filing100%€800.00
The 2026 tax year, as the return computes it
- Realized gains
- €8,000.00
- Net realized
- €8,000.00
- Exemption available
- €10,000.00
- Exemption used
- €8,000.00
- Taxable base
- €0.00
- Tax due @ 10%
- €0.00
Whichever route applies, the annual exemption and loss offsets are only settled through the tax return — withholding at source never applies them.
The link carries your figures: opened anywhere else, it shows exactly the same result.
How this number is reached
The year you typed is priced twice by the same tax engine. In the withholding column, the flat rate is taken off each gain as it is realized — without the annual exemption and without the losses that come later, because both exist only on the annual return. The return then recomputes the year: gains less losses, less the exemption, times the rate. What was withheld beyond that result is recoverable; what the return computes beyond what was withheld is still due. In the opt-out column nothing is taken during the year and the return's figure is paid in full.
The rate, the exemption and every broker position come from the site's configuration. Two things remain unverified: the exemption carry-forward mechanism (published sources disagree) and the exact date from which Belgian intermediaries were required to withhold. This page compares the two routes; it does not recommend one.
Frequently asked questions
What does opting out mean?
That your intermediary does not withhold the 10% at source. The tax does not disappear: you compute it and settle it through your own return. Clients of foreign brokers — DEGIRO, Interactive Brokers, Trade Republic — are in that position without ever having chosen it.
Is opting out cheaper or more expensive?
The rate is the same 10% either way. What differs is timing and paperwork: withholding at source applies neither the annual exemption nor later losses, so it can take more during the year than the return finally keeps — the difference comes back after filing.
Why would withholding take too much?
Because the €10,000 annual exemption and same-year loss offsets are only claimable through the tax return. A broker withholding at source takes the flat rate off each gain; if your year ends below the exemption, everything withheld is recoverable — by filing, not automatically.
Does a Belgian broker always withhold?
No. LYNX withholds the stock-exchange tax but runs the opt-out system for the capital-gains tax, so its clients declare it themselves. Withholding one tax says nothing about the other.
Which code does the declaration use?
The return codes for the first assessment year had not been published by FPS Finance when this page was last reviewed. Until they are, any code circulating elsewhere is a guess; the figures here describe amounts, not form fields.
Read more
- The Reynders tax was not abolished: how it stacks with the capital gains tax
The Reynders tax — 30% on the interest component of funds holding more than 10% debt claims — was widely declared dead in 2025, but the law of 6 April 2026 kept it. How the two taxes combine, with a worked example following the circular.
- A worked example: a DEGIRO investor with €50,000 in a world ETF, 2024–2026
One fictional investor, one accumulating world ETF, followed from purchase through the 31 December 2025 step-up to a partial sale in 2026 — with the TOB, the step-up value and the 10% capital-gains tax shown line by line.
- You are on the opt-out side of the capital-gains tax: what lands on you
Under opt-out nobody withholds the 10% for you. Three jobs move from your broker to you — and one of them cannot be finished yet, because the declaration codes have not been published.
Have your broker export to hand?
The calculator reads a full export and prices the whole year, position by position.
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