Tax Return Forms: Updates and deadlines for assessment year 2026

Overview

On 16 March 2026, the Royal Decrees establishing the tax return forms for the corporate income tax, the non-resident corporate income tax (companies) and the legal entities’ tax with regards to assessment year 2026 were published in the Belgian Official Gazette. As the tax return forms have now become available, it is possible to start preparing the tax returns for the current assessment year.

To enable timely and accurate preparation of the tax returns, you will find below a brief overview of the applicable filing deadlines.
 

Deadlines

For corporate income taxpayers, as well as for non-resident corporate taxpayers and legal entities with a financial year-end between 31 December 2025 and 28 February 2026, the tax returns must be filed no later than 30 September 2026.

If the financial year ends between 1 March 2026 and 30 December 2026 (inclusive), the relevant tax return must, in accordance with the general rule, be filed by the last day of the seventh month following the closing of the financial year. If this filing deadline falls on a Saturday, Sunday or public holiday, the next working day will be considered the filing date.
 

Faster Repayment

In line with previous years, tax returns resulting in a refund position will be treated with priority, provided they are filed early (i.e. typically no later than the end of August or beginning of September, with the exact date for assessment year 2026 still to be communicated).

Early filing can significantly expedite the refund process, with refunds generally being paid by the end of December at the latest (barring exceptions).
 

Filing Formalities

Corporate income tax returns, non-resident corporate income tax returns and legal entities’ tax returns must be filed electronically via de Biztax application, which is accessible through the MyMinfin portal. A link to the Biztax application is available under the ‘My tax return’ tab.

The functionalities of Biztax remain unchanged compared to prior years. Note that online filing is mandatory and that taxpayers no longer receive a paper tax return. Exceptions to this requirement can only be granted in very specific circumstances.

Given the significant penalties and the extended investigation and assessment periods that may apply in case of late filing, we strongly recommend starting the preparation of the tax returns in a timely manner.

Should you require any assistance with your compliance obligations, please do not hesitate to reach out to us or your dedicated person of contact.