If you want to avoid mistakes, unpleasant surprises with the tax authorities, and a few unnecessary emails with your advisor, there’s something you should do before the income tax campaign begins: check your tax data and take a look at your tax return outcome.
The good news is that you can already do it.
Since March, you have access to both your tax data and the 2025 income tax simulator, so you can get ahead and have a large part of the work done.
You can now check your 2025 income tax data
The Tax Agency already has the information it will use for your 2025 tax return ready. In other words, you can now log in and see exactly what they know about you: your income, withholdings, personal details, bank accounts, and more.
This is key to understand: the Tax Agency does not start from scratch. They work with data provided by third parties (Social Security, companies, banks, etc.).
But that doesn’t mean everything is correct.
That’s why checking this information is not optional if you want to avoid problems later.
Very important: Check your tax address (make sure it’s up to date in 2026)
This is where many people make a mistake.
Even though you’re preparing your 2025 tax return, what you need to verify is that your tax address is your current one in 2026, not the one you had last year.
If you’ve moved and haven’t updated it, the Tax Agency may still have your old address. What’s the problem? Any important notification might not reach you.
But there’s another equally important reason.
If you work with a tax advisor, having all your data properly reviewed (including your address) makes everything move much faster. Think about it: it’s not the same to receive a client with everything ready as it is to start by checking basic errors.
In fact, realistically speaking, an advisor will always prioritize clients who make their job easier.
An obvious example: imagine you send your reference number with everything checked and correct. They can start working on your tax return almost immediately. On the other hand, if they find errors or unchecked data, they’ll likely need to contact you, wait for your response, and delay the entire process.
How to access and manage your tax data
To access your actual tax data (not the simulator), you need to verify your identity.
You can do this in several ways: using Cl@ve, a digital certificate, electronic ID, or a reference number.
If this is your first time logging in for this tax income campaign, the Tax Agency will ask you to confirm or update your tax address before showing you your data. This is exactly the point where you should make sure everything is up to date.
Once inside, you’ll be able to check all the information the Tax Agency has about you and even check your tax data from previous years if needed.
Tutorial: How to change and check your tax data
Let’s go step by step on how to access, change, and check your tax data:
1. To begin, go to the Tax Agency website through this link. Here, you’ll need to identify yourself using the method that suits you best. For this tutorial, I’m logging in with my digital certificate (the second option):
Next, on the following screen, it asks me to choose whether I’m accessing to review my own data or on behalf of someone else. This second option can be used to check the data of your relatives and/or, if you’re a tax advisor, your clients.
I select Actuar en nombre propio and press on Confirmar.
2. Next, the system shows my tax address and the cadastral reference of my property. If I need to update this address because in 2026 (remember, not the 2025 address) I no longer live there, I would click on Modificar. In my case, I click on Continuar:
3. The next screen shows me the Identification Data (Datos identificativos) and the Tax Address (Domicilio fiscal) that I just checked and/or changed.
Next, the Tax Agency provides me with all the information they have about me:
– EMPLOYMENT INCOME
– ECONOMIC ACTIVITIES – here is a list of all my clients to whom I have withheld tax during 2025. This will appear if any of your activities are professional and you also invoice Spanish companies and professionals:
It’s important to verify that the withholdings match those you have documented in an Excel spreadsheet from 2025.
This is extremely important! If the withholding amounts don’t match, contact the company or professional to resolve the issue as soon as possible. If you file your tax return with discrepancies in these amounts, the Tax Agency will audit both you and your client to clarify this “numbers discrepancy.”
– BANK ACCOUNT INCOME – These are the bank accounts from which you have received any income.
– INFORMATION REGARDING PROPERTY DEPRECIATION DECLARED BY THE TAXPAYER IN 2024 – This section will contain the list of properties you declared on your 2024 tax return.
– INCOME FROM PROPERTY RENTALS – Note the message and you will see that the Tax Agency has no information on whether you rent out your properties. If you submit the draft return without reviewing it and adding this information, the Tax Agency will penalize you for not declaring this income.
– CENSUS DATA ON REGISTERED ECONOMIC ACTIVITIES IN 2025 – here are the activities you have been registered for with their respective IAE codes:
– CONTRIBUTIONS TO SPECIAL SOCIAL SECURITY SCHEMES AND SPECIAL AGREEMENTS – carefully check this information and the warning message. This is the sum of all self-employed contributions you have paid during 2025. Sometimes this figure does not reflect reality and must be corrected later in your tax return.
– LOANS AND CREDITS RELATED TO REAL ESTATE – here are the mortgages and loans you have
– CADASTRAL INFORMATION ON PROPERTIES – the cadastral references of the properties you own
– INFORMATION ON INCOME FROM EMPLOYMENT, CERTAIN ECONOMIC ACTIVITIES, PRIZES AND CERTAIN CAPITAL GAINS AND INCOME IMPUTATION, WITH A TAX YEAR PRIOR TO 2025
How to use the 2025 income tax simulator (Renta Web Open)
In addition to reviewing your data, you can go one step further and simulate your tax return.
For this, you have Renta Web Open, a tool from the Tax Agency that allows you to create a kind of draft without needing to identify yourself.
It’s important to clearly understand what it is, and what it isn’t.
It cannot be used to file your tax return, nor does it validate your real data. It’s simply a simulator where you manually enter information to see whether you’ll have to pay or receive a refund.
Another common mistake among those who were self-employed in 2025—even if only for one day—is assuming that the Tax Agency already has the data from your self-employed activity and submitting the draft directly.
Be very careful with this, because the Tax Agency does not include your self-employed data in this draft—only the data shown in the section above. It also does not include income and expenses from rental properties if you rent out homes or business premises.
Even so, it’s very useful to get an idea of where things stand, as long as you don’t take your self-employed activity into account.
When you access it, you can start a return from scratch or load one you previously saved. From there, you choose whether to run an individual or joint simulation and fill in the information requested by the system.
As you enter the data, you can see the result in real time. You can even generate a PDF preview, although that document has no legal validity.
How to get the reference number for the 2025 income tax campaign
The next step is to obtain your reference number, as it will allow you to access almost all the services available during the tax campaign.
Heads up, the reference number changes every year! This means the one you used in your previous tax return is no longer valid.
To get the new one, you’ll need to log in to the Tax Agency website using one of the usual methods or enter your National Identity Document (DNI) number along with the information from box 505 of your previous tax return (the third option in the image below).
If you didn’t file a 2024 tax return, you’ll need to provide an IBAN from one of the Tax Agency’s partner banks to obtain your tax return.
You can also do this through the Tax Agency’s app, which is usually the fastest option if you have it installed.
Once you enter the information correctly, the system will give you the reference number with this message:
You should also provide this number to your tax advisor if you will not file your tax return yourself.
Important warning: What NOT to do once you’ve started your tax return
Something we see every year as tax advisors during the income tax campaign is this: we get a client’s reference number, and shortly after, the client decides to “log in to see how their tax return is going.” To do that, they need to request a new reference number, so the previous one the advisor was using gets deleted. As a result, all the work done up to that point is lost.
That’s why, once you obtain this number and assign the work to your advisor, do not log in again unless you want someone else to continue your tax return. Your advisor should send you the final draft before submitting it, so you’ll be able to review everything before giving your approval.
Key dates for the 2025 Income tax campaign
The campaign starts on April 8 and ends on June 30, but there are several important dates to keep in mind depending on how you plan to file your return.
From April 8, you can file your return online.
If you prefer to do it by phone, you’ll need to request an appointment starting April 29, and they will call you from May 6 onwards.
For in-person assistance, appointments can be booked from May 29, with meetings starting on June 1.
And if your return results in a payment and you want to set up direct debit, be careful: the deadline is earlier—June 25.
Frequently asked questions about the 2025 Income tax campaign
Is it mandatory to check your tax data before filing your return?
It’s not strictly mandatory, but in practice, you should always do it. The Tax Agency works with data provided by third parties, which may contain errors or be incomplete. If you don’t check it and submit the draft directly, the responsibility will be yours, not the Tax Agency’s.
What happens if my tax address is not updated in 2026?
It may seem like a minor detail, but it’s not. If your address is incorrect, you might miss important notifications from the Tax Agency. Also, if you work with an advisor, having this detail wrong can delay your entire filing process. It may also cause issues if you want to apply for certain grants or specific tax benefits.
Do I need to provide my current address even though the return is for 2025?
Yes. Even though you’re filing for the 2025 tax year, you must ensure your tax address is your current one in 2026. This is the information the Tax Agency will use to communicate with you during the campaign.
Does the Tax Agency’s draft include my self-employed data?
No. This is one of the most important mistakes. If you were self-employed in 2025—even for just one day—the Tax Agency does not automatically include this data in the draft. It only shows data related to employment as an employee.
That’s why, if you submit the draft without reviewing it, you may be incorrectly declaring your income.
What is the Renta Web Open simulator used for?
It allows you to simulate your tax return and see whether you’ll have to pay or receive a refund. It does not validate real data or allow you to file your return. It’s simply a tool to help you get an early idea before the campaign starts.
Can I file my tax return through the simulator?
No, you can’t. Renta Web Open does not allow you to file your return. It is only for testing purposes. To submit your return, you need to access Renta Web with proper identification.
How can I access my tax data?
You can access it by identifying yourself using Cl@ve, a digital certificate, electronic ID, or reference number. Without identification, you can only use the simulator—not view your real data.
Is the reference number the same every year?
No. The reference number changes every year. The one you used in the previous campaign is no longer valid, so you’ll need to generate a new one for the 2025 campaign.
What do I need to obtain the reference number?
You’ll need your ID number and the amount from box 505 of your 2024 tax return. If you didn’t file last year, you’ll need to provide a valid bank account IBAN to obtain it.
Why is it important to have everything checked before sending your data to your advisor?
Because it makes their job easier. If your data is correct and already reviewed, your advisor can start working on your return sooner. On the other hand, if there are errors or unchecked data, they’ll need to stop, contact you, and that delays the entire process.
Get ahead and avoid problems
If you do just one thing after reading this article, make it this: log in, check your tax data, and make sure everything is correct—especially your current address.
With that, you’ve already completed half the work.
And if you also simulate your tax return, you’ll enter the campaign knowing what to expect—calm, prepared, and with an advantage.
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