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 a rate of 10% on the positive difference between the amount received and the relevant acquisition value. For financial assets acquired before 1 January 2026, the starting point 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 evidence of 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, deductible capital losses and a higher historical acquisition value that the taxpayer may be entitled to claim. These elements can instead be taken into account through the personal income tax return.

The withholding obligation generally rests with the Belgian intermediary involved in the 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. Where the taxpayer opts out, the relevant capital gains must be reported in the annual personal income tax return and any tax due will be collected through the assessment. The Belgian intermediary must nevertheless report certain information concerning the taxpayer and the relevant 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.

Impact on equity-based remuneration granted to your employees

The withholding tax mechanism may also have practical implications for beneficiaries of equity-based remuneration, including bank warrants, stock options, free shares and shares acquired at a discount. For more information on the application of the capital gains tax to such arrangements, please refer to our Alert.

From a withholding tax perspective, particular attention should be paid to where the financial assets are held and disposed of. This distinction may be particularly relevant where shares or other financial instruments resulting from an equity plan are held through a Belgian bank or through a foreign broker or financial institution. Where no Belgian intermediary is involved, the employer should ensure that the beneficiaries have sufficient information regarding the relevant transactions to calculate and report any taxable capital gain in their Belgian personal income tax return.