Tax ID on Invoice: EIN, VAT Number, TRN and NTN Explained

Quick answer: The tax ID on an invoice is the registration number that identifies your business to the tax authority: for example an EIN in the US, a VAT number in the UK and EU, a TRN in the UAE, or an NTN and STRN in Pakistan. If you are registered for VAT, GST or sales tax, showing your number is usually mandatory on tax invoices; for business customers, many regimes also require theirs. Place it in your business details block, labelled clearly.

This guide explains the main tax identifiers by country, when each must appear on an invoice, how to format them, and the mistakes that get invoices rejected. Our free invoice generator has a tax ID field for both you and your client, so you can follow along as you read.

Important: This article is general information, not tax advice. Invoice requirements and identifier formats are set by each country and can change. Confirm what you must show with your tax authority or a qualified adviser, particularly before your first invoice in a new country.

Tax IDs by country at a glance

Country	Identifier	Typical format	On invoices?
United States	EIN (Employer Identification Number)	9 digits, written XX-XXXXXXX	Not generally required; often shown for B2B
United States	State sales tax permit number	Varies by state	Sometimes expected; check your state
United Kingdom	VAT registration number	GB followed by 9 digits	Required on VAT invoices
EU member states	VAT identification number	Country prefix plus digits/characters, e.g. DE + 9 digits	Required on VAT invoices
United Arab Emirates	TRN (Tax Registration Number)	15 digits	Required on tax invoices
Pakistan	NTN and STRN	NTN issued by the FBR; individuals generally use their CNIC number	Both shown on sales tax invoices
India	GSTIN	15 characters	Required on GST invoices
Australia	ABN	11 digits	Required on tax invoices
Canada	Business Number with GST/HST account	9-digit BN plus program identifier, e.g. RT0001	GST/HST number required on qualifying invoices

United States: EIN and sales tax permits

An EIN is a nine-digit federal tax ID issued free by the IRS to businesses, including many sole proprietors who want one. There is generally no federal requirement to print an EIN on an invoice, and many small businesses do not. Others include it because business clients find it useful for vendor setup. The usual route for a client to get your tax details for reporting is Form W-9, not the invoice; see W-9 vs 1099 for contractors.

Never print a Social Security number on an invoice. Invoices are forwarded, stored and emailed widely, and an SSN on them creates identity theft risk.

If you collect sales tax, some states expect or allow your sales tax permit number on invoices, and buyers claiming an exemption will give you their certificate or permit numbers. See sales tax on invoices in the US. The USA invoice generator labels the field "EIN" by default.

United Kingdom and EU: VAT numbers

Once you are VAT-registered, your VAT number must appear on every VAT invoice you issue. UK VAT numbers are usually shown as "GB" followed by nine digits. EU VAT numbers start with a two-letter country prefix (Greece uses EL) followed by a national format that varies by country.

Some countries allow alternatives. Germany, for example, requires either the national tax number (Steuernummer) or the VAT identification number (USt-IdNr.) on invoices, and the VAT ID is the one used for intra-EU trade.

The customer's VAT number matters for cross-border B2B. For intra-EU reverse charge services and intra-Community supplies of goods, the customer's VAT number belongs on the invoice and should be validated through the EU's VIES service; HMRC offers its own checker for UK numbers. Our reverse charge invoice guide explains why. For the full field list on a VAT invoice, see the VAT invoice guide.

UK limited companies also have a Companies House registration number. UK company law requires certain company details, including the registered number, on business letters, order forms and websites, and many companies show it on invoices too. Your Unique Taxpayer Reference (UTR) does not belong on invoices. The UK invoice generator labels the field for a VAT number.

United Arab Emirates: TRN

A VAT-registered business in the UAE receives a 15-digit Tax Registration Number from the Federal Tax Authority. A full tax invoice must show the supplier's TRN and, in many cases, the recipient's TRN when the recipient is registered. Our dedicated guide to UAE VAT invoice requirements covers full and simplified tax invoices. Use the UAE invoice generator to get the TRN label and AED defaults.

Pakistan: NTN and STRN

In Pakistan, the National Tax Number identifies income tax registration with the FBR, and the Sales Tax Registration Number identifies sales tax registration. For individuals, the CNIC number is generally used as the NTN. A sales tax invoice normally shows the NTN and STRN of both supplier and registered buyer. Our guide to sales tax invoices in Pakistan covers the rest of the required fields, and the Pakistan invoice generator includes both labels.

Customer tax IDs: when to ask and how to verify

Your own number is only half the picture. For business customers, many VAT and GST regimes expect the buyer's registration number on a full tax invoice, and cross-border reverse charge invoices in the EU depend on it. In the US, buyers claiming a sales tax exemption give you an exemption or resale certificate rather than printing a number on the invoice.

The easiest time to collect a customer's tax ID is at onboarding, before the first invoice is due:

• Ask for the legal entity name exactly as registered, plus the tax ID, in your new-client form or first email.
• Verify it where an official checker exists: VIES for EU VAT numbers, HMRC's service for UK VAT numbers, and the relevant authority's lookup in other countries where one is available.
• Save a record of the check (a screenshot or confirmation reference) with the client file, especially for cross-border sales where the number justifies not charging VAT.
• Re-check periodically for long-running clients, because registrations can be cancelled.

If a customer cannot give you a valid number, do not guess. Ask your adviser whether you should charge local tax instead of applying a reverse charge or exemption.

Where to put the tax ID on an invoice

1. Your tax ID goes in your business details block, under your legal name and address, with a clear label such as "VAT No." or "TRN".
2. Your client's tax ID goes in the "Bill to" block under their legal name and address.
3. Label every number. A bare string of digits tells a reviewer nothing. Use the official term for the country.
4. Use the same format on every invoice, including the country prefix, so automated capture tools match you to the right supplier record.
5. Do not hide it in the footer in tiny type. Accounts payable teams look for it near the top.

Here is how a header might look for a UK VAT-registered business billing a German customer:

From	Bill to
Northfield Studio Ltd 12 Example Street, Leeds VAT No. GB123456789 Company No. 01234567	Beispiel GmbH Musterstraße 5, Berlin USt-IdNr. DE123456789

The numbers above are placeholders, not real registrations.

Common tax ID mistakes on invoices

• Showing a VAT or GST number before registration is confirmed, or after deregistration.
• Typos in your own or your customer's number, which can cost the customer their tax credit.
• Missing customer VAT number on a reverse charge invoice.
• Printing an SSN or other personal ID that does not need to be there.
• Using a different name on the invoice from the one the tax ID is registered to.
• Unlabelled numbers that leave the reader guessing which is which.

For the wider picture of what a tax invoice must contain once you are registered, read our tax invoice guide.

Add your tax ID to your next invoice

Open the invoice generator, enter your tax ID and your client's in the labelled fields, and download a PDF. The Corporate invoice template puts registration numbers where accounts payable teams expect to find them. Check the exact requirement with your tax authority before your first invoice in a new country.