Are you familiar with the most important dates in the 2026 IRS calendar? Although the annual tax return is only submitted between April and June, there are several important deadlines throughout the year that taxpayers should be aware of.

Missing one of these deadlines may affect your tax deductions, delay your tax refund, or even result in penalties.

To help you stay compliant, we’ve put together the key dates you should mark in your calendar.

IRS Calendar 2026: Important Dates for Filing your Tax Return

Compared with previous years, the IRS calendar remains largely unchanged. However, complying with each deadline is essential to ensure your tax return is processed correctly and that you avoid unnecessary issues with the Portuguese Tax and Customs Authority (Autoridade Tributária e Aduaneira – AT).

Below are the most important dates for the 2026 tax year (to be completed in 2027).

February 2027

Until 15 February, taxpayers must notify the Portuguese Tax Authority of any changes to their household composition.

This includes situations such as the birth of a child, children no longer qualifying as dependents,  marriage, divorce, the death of a spouse or any other change affecting the tax household. 

Keeping this information up to date ensures that your IRS return reflects your correct family circumstances.

Until February 28th,  by the end of February, taxpayers must validate and confirm all invoices recorded in the e-Fatura portal.

Self-employed individuals taxed under the Simplified Regime must also classify their business-related expenses as:

• Personal; 
• Business; 
• or Mixed use. 

This step is essential to ensure that all eligible tax deductions are correctly considered.

March 2027 

By 15 March, the Portuguese Tax Authority makes available the provisional calculation of tax deductions based on the invoices previously validated.

From 16 to 31 March,if you disagree with the deduction amounts calculated by the Tax Authority, you may submit a formal complaint (reclamação) through the Portal das Finanças.

Until 31 March, this is also the deadline for taxpayers wishing to allocate part of their IRS or VAT through the IRS Tax Allocation Scheme (Consignação do IRS/IVA).

Eligible organizations can be selected directly through the Portal das Finanças.

From 1 April to 30 June 2027

This is the official IRS filing period.

During these dates, all taxpayers must submit their annual IRS return, regardless of the type of income received.

Although the legal deadline is 30 June, filing early is generally recommended.

Submitting your return during the first few weeks often allows any tax refund due to be processed sooner.

Until 31 July 2027

By July 31st, the Portuguese Tax Authority must issue the official IRS Assessment Notice (Nota de Liquidação).

This document confirms the final tax assessment for the year and is issued to taxpayers who submitted their return within the legal deadline.

This is also the deadline for the Tax Authority to process IRS refunds for taxpayers entitled to receive one.

Unfortunately, not every taxpayer receives a refund.

If your IRS assessment results in additional tax being payable, payment must generally be made by 31 August, provided your return was submitted within the legal filing period.

Late submission may result in different payment deadlines together with interest and financial penalties.

Keeping track of the IRS calendar is one of the simplest ways to avoid unnecessary complications with your annual tax return.

By meeting each deadline, validating your invoices on time, and submitting your return promptly, you can maximize your available deductions and, where applicable, receive your tax refund as quickly as possible.

If you are unsure about any stage of the IRS process or need assistance completing your tax return, consult a Certified Accountant to ensure full compliance with Portuguese tax legislation.