The Portuguese NIF: what its nine digits tell you

What the NIF is, in nine digits

The tax identification number is, in the words of article 2 of Decreto-Lei 14/2013, «a sequential number intended exclusively for the processing of tax and customs information, to be generated automatically»¹. Sequential and automatic: the first eight digits are simply the order in which the number was issued, and they encode neither a date of birth, nor a place of birth, nor anything else about the person.

Two things, however, are not sequential. The last digit is an arithmetic check. And the first is a classification, fixed in law, of the type of holder. It is because of that second point that a Portuguese tax number is worth a closer look, and that is where most of this article goes.

The check digit, step by step

Article 4(1) says the NIF of individuals «is a number made up of nine digits, the first eight sequential and the last a control digit»¹. That a control digit exists is therefore law. How it is computed is written in neither decree-law: it is the modulus-11 rule the tax authority applies, and it takes four steps.

1. Multiply the first digit by 9, the second by 8, and so on until you multiply the eighth by 2. The weights are, in order, 9, 8, 7, 6, 5, 4, 3 and 2.
2. Add the eight products.
3. Divide the sum by 11 and keep the remainder.
4. The check digit is 11 minus that remainder. If the result is 10 or 11, the digit is 0.

With 123456789 the arithmetic is short: 1×9 + 2×8 + 3×7 + 4×6 + 5×5 + 6×4 + 7×3 + 8×2 gives 156. Dividing 156 by 11 leaves 2, and 11 minus 2 is 9, which is exactly the ninth digit. The number passes the check, and it is obviously made up. Keep this case, because it is the shortest proof of something many people read backwards: a correct check digit says nothing about whether the number exists.

The fourth step has a consequence that explains something odd. Since 11 minus 0 would be 11 and 11 minus 1 would be 10, and neither is a digit, the convention uses 0 in both cases. That means 0 comes from two possible remainders while each of the other nine digits comes from just one. If it seems to you that an unusual number of Portuguese tax numbers end in zero, you are not imagining it: it is the rule.

So what is the check good for? Exactly what it was designed for: catching a transcription error. Change one digit, or swap two neighbouring digits, and the weighted sum changes, the expected check digit stops matching, and the error is obvious. That is why a form that validates the NIF before submitting it saves months of corrections.

The first digit: who the holder is

This is the information almost nobody uses. Two decree-laws split the nine digits between them, and each covers a part.

On the individual side, article 4(2) of Decreto-Lei 14/2013 says «the leftmost digit may vary between the digits 1 to 4»¹. And paragraph 3 adds a fine rule that appears in almost no guide: «the leading digits 45 correspond to non-resident citizens who obtain in Portuguese territory only income subject to withholding tax on a definitive basis»¹. That is not an administrative curiosity. If you are about to pay someone whose NIF starts with 45, the decree-law itself is telling you they are a non-resident whose Portuguese income is taxed by withholding. A NIF starting with 44 or 46, by contrast, belongs to an ordinary individual.

On the entity side, article 11(1) of the same decree-law says the NIF of entities covered by the National Register of Legal Persons regime «corresponds to the Legal Person Identification Number (NIPC) assigned by that body»¹. And article 13(2) of Decreto-Lei 129/98 fixes that number's shape: «the NIPC is a sequential nine-digit number, the leftmost digit varying between the digits 5 and 9, excluding the digit 7»².

Notice what those two rules settle in passing: a Portuguese company does not have a separate NIF and NIPC. It has one number, and it is the same in both roles.

The finding: the digit 7 is the seam between the two registers

Put the two rules side by side and a conclusion appears that we could not find published anywhere with the citations beside it.

The National Register of Legal Persons is legally barred from using 7. This is not an internal practice or a statistical coincidence: article 13(2) excludes it in express words².

And 7 is exactly what the tax authority reserves for itself. Article 11(3) of Decreto-Lei 14/2013 says «the NIF to be assigned under paragraph 2 of this article begins with the digit 7»¹, and that paragraph 2 lists three cases: non-residents whose only Portuguese income is subject to final withholding, funds, and entities with obligations to the tax authority outside the register's regime. Article 16(2) repeats the same rule for undivided estates: «the NIF to be assigned begins with the digit 7»¹.

The practical conclusion is strong and immediately usable: a NIF beginning with 7 is never a company incorporated in Portugal. It is an undivided estate, a fund, or a non-resident entity. If you receive an invoice from a supposed Portuguese company with a number like that, either the number was miscopied or the entity is not what it claims to be.

The rest of the map for undivided estates is worth keeping, because that is the commonest 7 in a family's life. Article 16(1) gives exclusive competence to the tax authority, paragraph 3 says the request may be made by the head of the estate, their representative or a business manager, and paragraph 4 requires the estate's designation to contain «the name of the deceased followed by the expression head of the estate of»¹. For tax purposes, an undivided estate is an entity with a number of its own.

The digit 0, and what this article does not tell you

One digit is left over, and it resolves by subtraction. Individuals occupy 1 to 4. The register has 5 to 9 without the 7. The tax authority takes the 7. That leaves 0, which neither decree-law assigns to anyone. So a number starting with 0 cannot be a NIF, even when the arithmetic works out, and it does: 000000000 has a weighted sum of zero, a remainder of zero and a check digit of zero.

There is also something you will deliberately not find here, and the reason is stated rather than implied. The finer breakdown inside the 5 to 9 range, that is what distinguishes a 5 from a 6, an 8 or a 9, is not published on this page. Article 13(3) of Decreto-Lei 129/98 provides that «the assignment of the leftmost digit is carried out in accordance with a table approved by order of the Minister of Justice»², and that order is not readable from the primary sources we can reach. Lists of those correspondences circulate online, but none we can cite, and on a page about tax numbers we prefer an admitted gap to a plausible table.

Where a wrong NIF costs money

The question «is this NIF valid?» almost always has money behind it. It is worth seeing the three places where that happens.

On an invoice you issue. Article 36(5)(a) of the VAT Code requires the invoice to contain «the names, firms or company names and the registered office or domicile of the supplier of goods or provider of services and of the recipient or acquirer who is a taxable person, as well as the corresponding tax identification numbers»³. Both numbers, yours and the client's, and they are a mandatory element of the invoice, not an extra.

On an invoice you receive. Article 78-B(3) of the Personal Income Tax Code says «acquirers wishing to benefit from the tax credit must require the issuer to include their tax identification number on the invoices»⁴. And paragraph 5 explains why that is decisive: the value of the deduction «is computed by the Autoridade Tributária e Aduaneira on the basis of the invoices reported to it electronically, by the end of February of the year following their issue, in respect of each acquirer identified on them»⁴. If the number reported is not yours, the expense lands in someone else's e-fatura. That same paragraph 3 leaves a way out for invoices issued without a NIF: the acquirer can report them using the two-dimensional barcode, the QR code, or the unique document code.

On withholding tax. A NIF beginning with 45 or 7 is the statute's own warning that you are paying a non-resident, which changes the applicable withholding regime. A single leading digit tells you that before anything else does.

What the check does not replace

One limit needs to be clear. This check is arithmetic and local: it runs in your browser, queries no database, and the number never leaves the page. That is an advantage in privacy and a limitation in reach. If what you need is to know whether a NIF exists, is active, and whom it belongs to, that lives in the tax authority's register and is confirmed with them, on the Portal das Finanças. What this page does, and does well, is catch the error that happens far more often: a miscopied digit.