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.

What you need to know

•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.
•Legal framework: law adopted on 3 April 2026, published in the Belgian Official Gazette on 21 April 2026.

Opt-in or opt-out?

Opt-in (default): an intermediary established in Belgium withholds 10% at source.

Opt-out: you declare your capital gains yourself in your income tax return — to be notified by 31 August 2026 at the latest.

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.)

⚠️ Don’t confuse the two dates — 31 May 2026 = end of the transitional period (withholding starts 1 June). 31 August 2026 = deadline to notify your opt-out. These are two different things.

The Belgian investor’s other obligations

Benchmarkr sheds light

Aggregate your accounts, 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-out

Sources

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