How to file your income tax campaign with digital certificate

It has now been several weeks since the tax return filing period began, and with it have come questions from the public about how to complete it correctly, what the deadlines are, and what documentation is needed to avoid making mistakes when dealing with the tax authorities.

The good news is that it doesn’t have to be this way. Nowadays, many administrative procedures can be carried out from the comfort of your own home thanks to the digital certificate, a method designed to simplify and streamline the process. That is why today we are revealing the advantages of filing your income tax campaign using a digital certificate in 2026 compared to other forms of identification, and how we at Viafirma can help you manage your digital identity in a centralised, secure manner and, above all, without the usual technical complications at this time of year.

Why use a Digital Certificate for your income tax campaign?

When filing your tax return on your computer, you have various ways to identify yourself: Digital Certificate, Cl@ve Móvil/PIN, Reference Number, and Access to Draft and Data. Each of these methods has its own features and advantages that set it apart from the rest. However, our recommendation is that you always opt for the Digital Certificate: if you have it installed, it is the easiest, safest and quickest way to identify yourself. You don’t need to wait for codes or open external apps on your mobile. It is virtually impossible for someone to impersonate you, and it ensures that the tax return you submit is exactly the one that reaches the Tax Agency, without any alterations along the way.

It is also worth noting that the Cl@ve is primarily used to identify you, whereas the Digital Certificate enables you to electronically sign documents.

Therefore, if you need to submit an officially signed document that is not a standard form, the Digital Certificate is the right tool for the job.

Prerequisites before you begin

Before logging into the AEAT’s Electronic Office, you must ensure that your ‘digital environment’ is suitable. An error here will prevent the system from recognising your identity.

Browser compatibility and prior configuration

The first step you must take to file your 2026 Income Tax Return without any issues is to check that the browser you are going to use is compatible with the system. Otherwise, it will cause problems and will not recognise your identity.

Currently, the most stable browsers are Google Chrome and Microsoft Edge, which use the operating system’s certificate store (Windows or macOS). Mozilla Firefox, on the other hand, uses its own independent certificate store; and Safari works well on Mac provided the certificate is correctly installed in Keychain Access.

On the other hand, another equally important step is to check that it has been configured correctly. Although the settings can be viewed in various ways (pop-up window settings), the most important thing is that the AutoFirma software is installed: without it, you will not be able to file your tax return.

Key dates and deadlines for the 2025 Income Tax Return Campaign

Beyond the technical aspects, there is one fundamental point we must note and highlight on the calendar: the deadlines for submitting your Income Tax Return this year. Whilst some check their draft and submit their return on the very first day the window opens, others wait until the last few days, thinking they still have some leeway.

For this reason, it is important not to overlook the dates: this year, you can file your return from 8 April to 30 June 2026.

How to file your tax return with digital certificate

Filing your tax return using a digital certificate is simpler than it might seem. You simply need to follow the steps listed below:

Step 1: Access Renta Web

The difference between accessing the Online Portal using a digital certificate or via another method is explained here. On the Tax Agency’s website, search for ‘2025 Income Tax Campaign’ and select the option ‘Draft/Return Processing Service (Renta DIRECTA and Renta WEB)’. When choosing your login method, select ‘Digital Certificate or e-ID’. A pop-up window will open showing the certificates available on that computer; choose your certificate and click ‘Accept’.

Step 2: Reviewing tax details

From this step onwards, the process is the same as for the other identification methods. Your draft tax return will appear immediately, but it is not infallible and may contain certain errors. We therefore recommend that you check your personal and family details, mortgages and bank accounts, and ensure that the amounts shown as employment income match the withholding tax certificate provided by your employer.

Step 3: Common amendments

When submitting your tax return, you may be eligible for certain special boxes, but these are usually left blank. This applies to regional tax deductions, changes of address, trade union dues and professional association fees.

Step 4: Sign and submit

After checking all the information, you must click on ‘Submit return’ and provide a final confirmation. Finally, download the proof of submission as a PDF.

Common errors when using a digital certificate on the Online Portal

As you have seen, filing your tax return using a digital certificate is easy and intuitive in 2026; however, on occasion, you may encounter problems partway through the process that prevent you from completing the procedure this way.

Some of the most common problems we may encounter are:

• Certificates that have expired or are not installed correctly. On a personal level, we use the digital certificate when we need to complete a procedure or access the Electronic Office. However, as we only use it when strictly necessary, it may have expired without us realising. If this is the case, the system will display an error and it will not be possible to use it. Problems can also arise if the certificate is not installed correctly.
• Electronic signature issues on the AEAT platform (AutoFirma). During the final step of the process (Sign and send), the system may freeze and fail to complete the process. This usually occurs because the browser lacks the necessary permissions to launch the application, because AutoFirma is not installed, due to antivirus blocking, or because of Java incompatibilities.

How to avoid expired certificates and compatibility issues with Viafirma

Filing your tax return using a digital certificate is the quickest and most convenient option, but have you ever wondered what it would be like to do it from anywhere, including your favourite café? With Viafirma, it’s possible.

With over 25 years’ experience, we offer digital solutions designed to make your day-to-day life easier, including centralised management of digital certificates in the cloud. With us, you’ll no longer have to carry your certificates on physical tokens, with the significant risk that entails. You’ll be able to access the online portal of any public body from anywhere via your mobile, without needing a computer, with full legal validity and maximum security.

Furthermore, if your work involves dealing with mountains of documents or you’re responsible for signing them on a daily basis, you can also integrate our tools into your workflow. Regardless of the sector or department you’re in, you’ll be able to sign your documents electronically: from new employee contracts to confidentiality agreements, for example.

Submit your personal and business paperwork from anywhere

Would you also like to submit not only your tax return using a digital certificate, but all kinds of personal and corporate paperwork? Then put your trust in Viafirma. You’ll be able to electronically sign documents such as tenancy agreements and even informed consents, amongst many others, without having to rely on a physical office or travel.

What are you waiting for? Take your digital identity with you wherever you go. Contact our sales team today and complete paperwork in minutes, not weeks.