Taxes
Capital gains 2026: the 10% choice that can cost you.
From 2026, Belgium taxes capital gains on financial assets at 10%, on gains realized from 1 January 2026. Behind this single rate lies a little-known choice — opt-in or opt-out — that changes what you actually pay. And a deadline: 31 August 2026.
The 2026 capital-gains tax, in brief
- •Rate: 10% on capital gains realized from 1 January 2026.
- •Exemption: €10,000 per person per year, indexed (up to €30,000 for a couple). The unused part of the first bracket can be carried forward up to 5 years, capped at €15,000.
- •Transitional period: from 1 January to 31 May 2026, no withholding at source; withholding by Belgian intermediaries starts on 1 June 2026.
- •An annual choice: your option rolls over automatically from one year to the next. It stays revocable — once per taxable period — and any change only takes effect from the following period.
- •Legal framework: law adopted on 3 April 2026, published in the Belgian Official Gazette on 21 April 2026.
The silent trap of withholding at source
From 1 June 2026, your online bank or your platform established in Belgium starts withholding 10% on your capital gains, directly at source. That is the default regime, opt-in. Convenient, on the face of it: you have nothing to do. The problem is what that withholding does not do. The intermediary deducts indiscriminately, transaction by transaction, account by account. It does not apply the €10,000 per-person exemption you are entitled to each year, and it does not offset losses you realised elsewhere. Each platform withholds on its own, with no overall view of your situation.
The result is mechanical: you pay too much, and you tie up cash. That overpayment is not lost, but you only recover it much later — when you file, so around 2027 for 2026 income. In the meantime, the tax office holds your cash, not you.
Opt-in or opt-out: the real difference
On a foreign platform, no Belgian intermediary withholds for you: you are in self-declaration anyway.
Why opt-out is often more advantageous
- •The €10,000 exemption is not applied at the withholding stage: under opt-in you only recover it later, via your return. In the meantime, you have advanced money to the tax office.
- •Withholding is done by each Belgian intermediary separately; self-declaration lets you apply the exemption and account for your overall situation.
- •Under opt-out, you can offset your capital losses against your gains via the return.
- •Cash flow: no flat withholding that you then have to claim back.
A worked example (illustrative)
You realize +€12,000 of gains on one platform and −€3,000 of losses on another. Under opt-in, 10% is withheld on €12,000 = €1,200 advanced, ignoring the loss and the exemption. Under opt-out, your real base is €9,000, below the €10,000 exemption → nothing to advance. (Simplified example, to be confirmed for your situation.)
A legal framework still in motion
The subject is young, and the practical arrangements keep evolving. That instability is, in itself, a further argument for opt-out: keeping control of your return leaves you the flexibility to adjust your position as the framework firms up, rather than being subject to an automatic withholding that is hard to correct mid-year.
The Belgian investor’s other obligations
- Stock-exchange tax (TOB): does your platform pay it? →
- Reporting a foreign securities account (CPC/NBB) →
Benchmarkr sheds light
Bring your transactions together, track your gains and losses, compute what you actually owe and compare opt-in / opt-out: Benchmarkr periodically prepares this view from your aggregated transactions.
Compare opt-in and opt-outSources
- FPS Finance — Capital-gains tax
- RSM Belgium — Capital-gains tax law (key features)
- Degand & Partners — 2026 transitional regime
- Wikifin (FSMA) — taxes on your investments
Benchmarkr is an assistance and calculation tool. It does not constitute personalized tax advice. Rules may change; check your situation with a professional. Updated: 2026