Northern Ireland VAT number: format and validation

By Remco from Avatcado

Format

XI followed by 9 or 12 digits. The local term is VAT registration number (VAT Reg No, English).

Pattern: /^\d{9}(\d{3})?$/

  • Same digits as the trader's GB VAT number with XI substituted for GB; it is an add-on to the UK VAT registration, not a separate one
  • Used by Northern Ireland traders for goods moving between NI and the EU under the Windsor Framework; services stay under UK-only VAT rules and use GB
  • XI numbers validate in VIES; GB numbers were removed from VIES on 1 January 2021

Example of a registered number: XI 510 4813 31

Check digit

Northern Ireland VAT numbers carry a check digit (MOD 97 / MOD 9755): Same check as the underlying GB VAT number: weights 8 down to 2 over the first 7 digits, with the last 2 digits as the check (the 9755 variant adds 55 before reducing).

Check a Northern Ireland VAT number

Checks route through VIES. Caching is enabled by default. Read the source, original result time and freshness label alongside validity; a cached or stale result does not freshly confirm current registration.

Enter a VAT number to see its registration result, source and freshness

Validate via API

The same validation as an API call, with the example number above:

curl "https://api.avatcado.com/v1/validate?vat_number=XI510481331" \
  -H "Authorization: Bearer avat_live_your_api_key"
import Avatcado from "@avatcado/node";

const avatcado = new Avatcado("avat_live_your_api_key");
const { data, error } = await avatcado.vat.validate({
  vatNumber: "XI510481331",
});

if (data?.data.valid) {
  console.log(`Registered: ${data.data.company?.name}`);
}

Free tier includes 500 validations per month. Get an API key or read the API documentation.

How Avatcado validates Northern Ireland numbers

  • Primary source: VIES.
  • Company name and address: yes, observed 2026-09-04.
  • When VIES is down: the most recent cached result, then a refunded 503.

See the full coverage table.

Frequently asked questions

When should a business use its XI number instead of GB?

Only for goods transactions involving Northern Ireland under the EU VAT rules that still apply there: NI-EU supplies, acquisitions, and related listings. Services and GB-internal trade always use the GB number.

How do I validate an XI VAT number?

Through VIES, which treats XI as a member-state code; HMRC's own checker covers the same registration under its GB form. A number can be valid as XI and the identical digits valid as GB simultaneously, because it is one registration.

How does Avatcado validate Northern Ireland VAT numbers when VIES is down?

For Northern Ireland VAT numbers, uncached checks use VIES, the EU's VAT Information Exchange System, which routes the query to Northern Ireland's own national database. Caching is enabled by default without a requester VAT number. Read the freshness label and original result time to distinguish a new lookup from a previous result. A valid answer includes the registered company name and address that Northern Ireland's tax administration publishes through VIES, which we last confirmed against a real registered number on 2026-09-04. No national register is published for Northern Ireland that Avatcado can consult as a substitute, unlike the ten EU countries with a national fallback on Pro and Business, so an availability fault such as MS_UNAVAILABLE or a timeout can be answered only by eligible cache. A stored result has meta.cached: true and meta.source_status: "unavailable", plus meta.stale: true when it is past the cache window. Requester checks disable stored responses by default; cache=true opts back in. If no eligible stored result can answer, the request returns a refunded 503 (upstream_member_state_unavailable). A cached or stale result is earlier registration evidence, not a fresh check.

Related guides

VAT rate in Northern Ireland

The standard VAT rate in Northern Ireland is 20%. Reduced rates: 5%, 0%. Northern Ireland uses UK VAT rates. See all Northern Ireland VAT rates.

Sources