Capital gains tax: circular on withholding tax obligations

On 20 October 2026, the Belgian tax administration published Circular 2026/C/94 (Dutch | French) on the withholding tax obligations arising in connection with the capital gains tax on financial assets. It follows Circular 2026/C/74 of 22 July 2026 (Dutch | French) on the personal income tax treatment of capital gains and focuses specifically on the withholding tax aspects of the new regime.

Key aspects of the circular

Scope of withholding at source

Withholding at source applies to Belgian resident individuals in respect of capital gains realised in the normal management of their private assets on certain financial instruments, insurance contracts and capitalisation transactions. Internal capital gains and capital gains on substantial shareholdings are not subject to withholding at source.

Withholding base and collection mechanism

The withholding tax is calculated at 10% on the positive difference between the amount received and the relevant acquisition value. For financial assets acquired before 1 January 2026, this is generally their value on 31 December 2025. Specific rules apply to insurance contracts and capitalisation transactions. Where the withholding agent does not have sufficient information on the relevant acquisition value, withholding may apply to the full amount received.

The withholding calculation does not take account of certain elements that may reduce the tax ultimately due, including the available exemptions, capital losses and, until the end of 2030, a higher historical acquisition value that the taxpayer may be entitled to claim. These elements can be taken into account through the personal income tax return.

The withholding obligation generally rests with the Belgian intermediary involved in the payment or transaction. For insurance contracts and capitalisation transactions, the Belgian insurance company paying the benefits is responsible for withholding the tax.

Opt-out and information reporting

Taxpayers may opt out of withholding on an account-by-account or contract-by-contract basis. They must then report the relevant capital gains in their annual personal income tax return and pay any tax due through the assessment. The relevant intermediary will nevertheless report certain information concerning the taxpayer and the capital gains to the Belgian tax administration.

The opt-out remains applicable until revoked. A revocation may be made only once per taxable period and takes effect from the following taxable period.

Transitional rules for 2026

The withholding obligation applies as from 1 June 2026. For capital gains realised between 1 January and 31 May 2026, taxpayers could request their Belgian intermediary to pay an amount equivalent to the withholding tax, provided the request was made by 31 August 2026. The equivalent amount must be paid by 30 November 2026. Importantly, a request for payment of this equivalent amount is treated as a decision not to apply the opt-out regime for the entire income year 2026.

Entities subject to legal entities tax

Certain Belgian entities subject to legal entities tax may also be liable to the capital gains tax on financial assets. Unlike the withholding mechanism applicable to individuals, the relevant withholding tax is, in principle, payable by the entity itself rather than withheld by a financial intermediary. The tax applies at a rate of 10% to the relevant capital gains, subject to the applicable scope and exemptions.