Model 1 (ISTG): What is it and how to deliver it?

Form 1 is the form that scares many people, but it is actually a normal step in any inheritance process.

The ISTG (Stamp Duty on Gratuitous Transfers) is a tax that may apply to inheritances and donations, with a rate of 10% in cases where the tax is applicable. The good news is that there are important exemptions for immediate family members, such as spouses, children, and parents. Even so, even when an exemption exists, reporting to the tax authorities remains mandatory.

This declaration is used to report the death and declare the assets. As a general rule, it must be submitted to the Tax Authority's website by the end of the third month following the month of death. When someone dies and there are assets, the Tax Authority needs to be informed. And that is precisely what Form 1 is for: to report the gratuitous transfer of assets upon death and to submit a list of assets.

This guide will explain what this declaration is, who needs to submit it, the deadlines, the documents you need to prepare, how to submit it on the Tax Authority's website (and alternatives), and the most common mistakes. The goal is simple: to help you submit Form 1 safely and without unnecessary complications.

What is Model 1 (ISTG)?

Form 1 is the Stamp Duty form for gratuitous transfers. In simple terms, it is the declaration used to notify the tax authorities that a transfer has occurred due to death and to identify:

• Who passed away.

• Who are the heirs?.

• What goods exist?.

• What values should be considered for tax purposes?.

It is normal for certain heirs to be exempt from Stamp Duty (for example, spouses, common-law partners, descendants, and ascendants, depending on the applicable rules). But even with exemption, Form 1 is usually required to regularize the inheritance. If you want to understand the phase before the division of the inheritance, see: unpartitioned inheritances.

When is it mandatory to submit Form 1?

Form 1 must be submitted when there is a gratuitous transfer of assets upon death, that is, when there are assets to be transferred to the heirs.

In practice, it is mandatory whenever there are significant assets to declare, such as:

• Property.

• Bank accounts and deposits.

• Vehicles.

• Social participations.

• Investment balances, securities and other assets.

Even if the family is not yet certain "what exists," the correct course of action is to gather information, request certificates and statements, and only then submit Form 1 with a consistent list of assets.

To organize the survey: How to find out about the assets of a deceased person.

Who files the tax return?

Generally, the person who submits Form 1 is the head of the household. This is the person who manages the inheritance until the division of assets and who has the duty to handle essential matters.

This is important because this contribution is not "for each heir individually." It belongs to the estate as a whole. The head of the estate contributes, and the heirs benefit from having their tax situation regularized.

If there is any doubt about legitimacy and initiative, the following may help: Who can initiate the sharing of assets.

Delivery deadlines

The deadline is one of the most stressful aspects. In practical terms, the application must be submitted by the end of the third month following the month of death. It's not "90 days from the date of death." It's counted in full months.

Simple example:

• Died on 10 January.

• The month of death is January.

• The following three months are February, March and April.

• The deadline ends at the end of April.

If you want to understand the impact of deadlines on the overall process: How long does the inheritance process take?.

Before you deliver: the step that many people ignore.

There's a practical detail that usually blocks everything.

In many cases, to submit Form 1, it is first necessary to request the Tax Identification Number (NIF) of the undivided inheritance. Without this tax identification number for the inheritance, the Tax Portal may not allow you to proceed, and the Tax Office may request that the registration step be completed.

If you want to understand how to handle this step: Tax Identification Number (NIF) for undivided inheritance: how to apply.

What documents should I prepare for submission?

The more complete the file is, the fewer additional requests arise and the faster this stage is completed.

• Death certificate.

• Identification of the deceased (Tax Identification Number and identification details).

• Identification of the estate administrator.

• Identification of heirs (Tax Identification Number and civil identification).

• Qualification of heirs, when already available.

• Bank statements and balance statements as of the date of death.

• Property registration books and/or title deeds for real estate.

• Vehicle documents (vehicle registration).

• Information regarding corporate participation, if any.

Qualification is often a crucial factor for banks and the organization of the process: Grant of probate.

How to fill it out without complicating things?

Form 1 serves as the "cover" of the process. Then there are attachments detailing assets and their relationship to heirs. It's not a guessing game. It's a declarative document that must be aligned with documentary evidence.

Completing Form 1 typically involves:

• Identification of the deceased.

• Identification of the estate administrator.

• Identification of the heirs.

• Listing of goods by category.

• Submission of applicable attachments (e.g., assets and identification of heirs).

To understand how to organize assets and valuables: list of assets in the inheritance.

How do I submit it through the Tax Portal?

For many families, the quickest option is online delivery.

Before we get to the list, a practical tip: submit your work early and keep proof (PDF or printout) of what you submitted.

Typical step-by-step guide for submitting Form 1 on the Tax Authority's website:

1. Log in to the Finance Portal with the head of household's credentials.

2. Go to Citizens.

3. Access Services.

4. Look for the area “Model 1 ISTG”.

5. Select the option to fill out and submit the entry.

6. Attach information or fill in attachments when requested.

7. Submit and save the receipt.

If a pending validation message appears, do not ignore it. It usually means that some data or an attachment is missing, or that there is an inconsistency between the identification and registration information.

Alternatives when the portal doesn't help.

The Tax Portal isn't always the easiest way to go, especially when:

• There are particularities (heirs abroad, incapacitated individuals, complex assets).

• The registration is not up to date.

• The inheritance tax identification number (NIF) has not yet been assigned.

In these cases, it may be possible to submit Form 1 through the online portal, attaching documents and explaining the situation, or in person at a Tax Office, ideally by appointment.

Delivery and banks: why does proof of payment matter?

Many families only remember Model 1 when they try to access their bank accounts.

Banks typically require proof of heirs and proof of tax compliance. Proof of submission of this declaration, along with heirship documents and identification, helps to expedite applications and reduces refusals.

If your immediate goal is to unlock funds: how to access the bank account of a deceased person.

Common delivery errors

Most delays don't stem from bad faith. They stem from a lack of continuity.

Before we get to the list, remember: Form 1 must match the documents and registration.

• Submitting a claim without having the inheritance tax identification number (NIF) when it is required.

• Indicating heirs with the wrong NIF or outdated data.

• Declaring assets without supporting documentation.

• Forget about assets that generate income (e.g., rents).

• Do not keep proof of submission.

• Trying to "fix it later" without realizing that this can trigger a new validation process.

What happens after delivery?

Submitting this declaration is not "the end of the inheritance." It is the closing of the tax reporting phase of the death.

From here, the family usually moves on to:

• Organization of assets, expenses, and income during an undivided inheritance.

• Valuation of assets for the purpose of division of property.

• Share by agreement where possible.

• Inventory, when there is a blockage.

For the path by agreement and the general sequence: How to share an inheritance. If there is a deadlock or dispute, it may be necessary to proceed through formal channels. Judicial division of inheritance.

And what happens when there are debts?

When there are associated debts, filing Form 1 remains important, but the overall strategy changes.

Debts discovered late can ruin deals.

• Map your liabilities early.

• Avoid hasty decisions regarding withdrawals.

• Document payments and reimbursements made from the estate.

For practical framing: How to share inherited assets with debts.

Quick checklist for stress-free delivery.

Before making the list, use this checklist as a final check.

• I have a death certificate.

• I know who the head of the household is.

• I have a tax identification number (NIF) and identification of heirs.

• I have bank statements and balances as of the date of death.

• I have documents for real estate and vehicles.

• I have the tax identification number (NIF) for the undivided inheritance, if needed.

• I have everything organized for attachments.

• I will keep proof of delivery.

Conclusion

This form should not be seen as "just another piece of paper." It is a strategic step that provides predictability to the process and reduces bottlenecks with banks, registries, and data sharing.

When the family tackles this stage early, with complete documentation and consistent values, the process ceases to be a marathon of going from counter to counter and becomes a plan. And, with everything properly submitted and supporting documents saved, it becomes much easier to move forward with banks, registries, and inheritance without new obstacles.

If you want to resolve this safely and avoid mistakes that cost months, talk to our experts. Probate and inheritance lawyers.