Sibylle Greindl

19 May 2026

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Capital gains tax in Belgium: opt-in or opt-out?

Belgium introduced a capital gains tax on financial assets in 2026. As a Belgian investor, you can choose how that tax is collected: through opt-in, where your financial institution withholds it directly on each transaction, or through opt-out, where you declare your capital gains yourself in your annual tax return. What do these two options actually involve? What are the advantages and drawbacks of each? And which one suits your situation? This guide walks you through the key considerations so you can make an informed decision.

How the capital gains tax on listed financial assets works

The capital gains tax applies to individuals who realise a capital gain when selling a financial asset. That gain is taxed at 10%. The tax applies retroactively from 1 January 2026.

Key points:

• A 10.000€ exemption applies to the first tranche of capital gains realised in any given calendar year.
• If an investor realises little or no capital gain in a given year, the first 1.000€ tranche of the exemption can be carried forward to the following year, for up to five years, giving a maximum total exemption of 15.000€.
• Capital losses can be deducted from capital gains realised in the same year. They cannot be carried forward to the following year.

Opt-in or opt-out: what do these terms mean?

"Opt-in" and "opt-out" refer to the choice the Belgian taxpayer has over how the capital gains tax is collected.

Until now, Belgian financial taxes such as the withholding tax on investment income (roerende voorheffing), the securities transaction tax (beurstaks), and the securities accounts tax have all been collected at source by the financial institution.

For the capital gains tax, the legislator introduces a new option. The taxpayer can choose between:

• allowing the financial institution to withhold the tax at source, as it normally does (opt-in),
• declaring gains directly through the personal income tax return (opt-out).

The pros and cons of opt-in

1. How opt-in works

Under opt-in, the financial institution calculates and withholds the capital gains tax on each transaction and remits it directly to the tax authorities.

2. Advantages of opt-in

Opt-in provides a degree of fiscal peace of mind:

• You do not need to track every financial transaction that contributed to a capital gain.
• You are protected against missing a payment you owe to the tax authorities.
• You do not need to set aside funds in anticipation of a tax bill.

Opt-in also offers a degree of privacy: the financial institution shares with the state only the total tax amount, without disclosing details of the individual transactions that generated a gain.

3. Disadvantages of opt-in

Opt-in does not eliminate all administrative obligations. To claim the exemption on the first 10.000€ of capital gains, or to deduct capital losses, you will still need to report them in your tax return.

In addition, each financial institution withholds 10% of every gain, per securities account separately, without accounting for any losses or exemptions. You are effectively pre-financing the state, potentially for more than two years if the tax assessment notice arrives late.

The pros and cons of opt-out

1. How opt-out works

Under opt-out, you report your capital gains to the tax authorities through your personal income tax return. In parallel, financial institutions report all of your transactions to the tax authorities.

You pay the tax via the tax assessment notice.

2. Advantages of opt-out

With opt-out, you benefit from the exemption from the outset:

• You pay the exact amount owed at the right time, via the tax assessment notice.
• You do not pre-finance the tax, unlike opt-in where it is withheld at source.
• You may not owe anything at all: this is the case when your realised gains stay below the 10.000€ threshold and/or when you have also realised capital losses during the same period.

Since you are declaring your gains in any case, you will naturally deduct your losses at the same time and claim the exemption on the first 10.000€ of net capital gains.

3. Disadvantages of opt-out

Opt-out requires discipline. Choosing opt-out means tracking and declaring all transactions. That can be a real obstacle for those who do not normally file a tax declaration, such as minor children, or when the amounts involved are modest.

You also need to set aside the calculated tax amount ahead of the tax assessment notice. There is always a risk of spending those funds in the meantime and finding yourself short on liquidity when the bill arrives.

Finally, investors with complex wealth management situations risk overlooking a gain they should have declared, exposing themselves to a tax adjustment.

Which option is right for you?

The choice depends on your personal situation and preferences. In both cases, you will need to go through the tax return to claim the exemption on the first 10.000€ tranche and deduct any capital losses.

If you choose opt-in, you have no risk of a tax adjustment and no need to set aside funds. The trade-off is pre-financing any overpayment, which you recover provided you complete your tax return correctly. For investors with complex portfolios, or those who value administrative simplicity above all, opt-in may be the better choice.

If you choose opt-out, you pay exactly what you owe, the full amount owed, and only that amount, when the tax assessment notice arrives.

Easyvest's passive, index-based approach keeps transactions to a minimum. A portfolio with low rebalancing, topped up by regular contributions, gradually accumulates gains that are only realised and taxed when a full or partial sale takes place. In that context, tracking transactions for capital gains tax purposes is straightforward. If your personal organisation allows for it, opt-out can be an excellent choice.

When does capital gains tax apply in an Easyvest portfolio?

A capital gain or loss is realised when a financial asset is sold.

In practice, a sale in an Easyvest portfolio occurs in the following situations:

• a withdrawal from the portfolio, which requires selling some or all of the assets. This may happen at the client's explicit request or automatically in the context of a drawdown portfolio.
• a portfolio rebalancing, when the actual risk profile has drifted from the target or recommended risk profile. Easyvest carries this out automatically as part of its management mandate.
• a partial sale to generate sufficient liquidity.

Any capital gain or loss realised through these operations falls within the scope of the capital gains tax.

Key dates for capital gains tax in 2026

The law came into force during 2026, which creates a slightly unusual calendar. Here are the dates to keep in mind and the decisions to make:

The 2027 tax return (tax year 2026): a key deadline

In 2027, you will file your tax return for 2026 and, for the first time, declare your capital gains and losses. It is in your interest to handle this correctly, even if you chose opt-in and it is not strictly required.

An example in figures:

By the end of 2026, you will have realised 15.000€ in capital gains on part of your portfolio and 2.000€ in capital losses on another part.

What is the tax impact, whether you chose opt-in or opt-out?

• Under opt-in, a 10% tax was automatically withheld each time a gain was realised during 2026. You will have paid 1.500€ in tax in 2026 for the 2026 tax year. Through your tax return, you can recover the 1.200€ that was withheld in excess, once your tax assessment notice arrives.
• Under opt-out, you realise gains and losses throughout 2026. In your 2027 tax return, you declare the amounts: 15.000€ in gains minus 2.000€ in losses, giving 13.000€ in net capital gains. The first 10.000€ of those 13.000€ is exempt. The 10% tax applies to the remaining 3.000€, meaning 300€ to set aside and pay via the tax assessment notice.

In this example, declaring all gains and losses allows opt-in investors to recover the 1.200€ overpaid, and opt-out investors to provision the exact amount that will appear on the tax assessment notice.

Joint accounts: opt-in or opt-out?

If you are married or in a legally registered partnership and hold a securities account in both your names, you must reach a unanimous decision between opt-in and opt-out.

Opt-in applies by default from 1 September 2026 if one partner does not communicate a preference.

Each account holder benefits from their own 10.000€ exemption on the same securities account. In other words, a couple can, after deducting losses, realise 20.000€ in tax-free capital gains on a single joint account.

If each partner holds a separate personal account, they may each choose their preferred option independently.

Jointly held assets: opt-in or opt-out?

As with a couple, the choice between opt-in and opt-out requires unanimous agreement among all co-owners. If one co-owner requests opt-out while the others prefer opt-in, opt-in prevails.

Each co-owner retains their annual 10.000€ exemption. Three co-owners therefore have a combined exemption of 30.000€ per year. Capital losses reduce each co-owner's taxable tranche in proportion to their share of the jointly held assets.

When a regular income is drawn through successive asset sales:

• opt-in means the tax is withheld at source at the point of each income payment, and recovered through each co-owner's individual tax return.
• opt-out means each co-owner pays the capital gains tax on their share of the jointly held assets via their individual tax assessment notice.

This income may flow to a usufructuary (a parent, for example) who donated their portfolio to their heirs, who hold it as jointly owned assets.

In that situation, opt-out can create an imbalance: the usufructuary receives a net income payment, while the co-owners end up funding the tax and having their 10.000€ exemption eroded.

Opt-in may be the more equitable choice in this case.

Minor children: opt-in or opt-out?

The child's legal representative makes the choice between opt-in and opt-out on the child's behalf.

Under opt-in, the legal representative can file a declaration so that the child benefits from the tax exemption on the first 10.000€ of capital gains.

Under opt-out, the legal representative is required to file a tax return in the child's name, declaring capital gains and losses.

"In practice," explains Corentin Scavée, co-founder and Head of Wealth Management at Easyvest, "the best approach is to opt for an account with low rebalancing and to top it up regularly. As long as there is no sale, there is nothing to declare."

In many cases, opt-in will be the most practical choice, particularly when the amounts to recover are modest.

Multiple securities accounts: opt-in or opt-out?

The opt-in or opt-out choice is made per securities account. The exemption on the first 10.000€ of capital gains, net of any losses, is linked to the individual and applies across all of their securities accounts combined, whether joint, co-owned, or personal.

In practice, someone might choose opt-in for a co-owned account and opt-out for a personal account.

Regardless of the financial institution involved, if no choice is communicated: opt-out applies for the first five months of the year and opt-in for the last seven months of 2026.

Conclusion

Opt-in or opt-out: if you file your tax return correctly, the financial outcome for your personal finances is the same either way.

Your primary concern should be making the choice that best fits your personal situation and preferences.

Whatever you decide, keep in mind that Easyvest's passive management approach keeps transactions to a minimum, which makes tracking them significantly simpler. Our team is available to guide you through your options and support you at each stage of the process.

Book an appointment with your Easyvest manager to review your personal situation (couple, co-ownership, children, transaction volume) and make your choice with complete confidence.

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