A VAT/GST registration number is the unique identifier a tax authority assigns to a business that is required to collect and remit Value Added Tax or Goods and Services Tax. It ties every sale you charge tax on, every purchase you reclaim tax on, and every return you file to a single account the government can audit. If you sell into a country that operates a consumption tax, this number is what lets you legally charge the tax, recover the tax you pay on your own inputs, and prove to customs and customers that you are properly registered.
“VAT” is the standard term in Europe, much of Africa, and parts of Asia. “GST” is used in Canada, Australia, India, and New Zealand, among others. The mechanics are the same: a multi-stage tax where each business in the chain collects on its sales and reclaims what it paid on its purchases, with the final consumer bearing the full cost.
When You Have to Register
Not every business needs a number. Whether registration is mandatory depends on how much you sell, what you sell, and where your customers are.
Sales Thresholds
Most countries set a turnover threshold. Cross it over the measured period and you must register; stay below it and you generally cannot charge the tax, but you also cannot reclaim the tax on your own purchases.
The numbers vary widely. In the United Kingdom, you must register when your taxable turnover exceeds £90,000 over the preceding 12 months, or when you expect to exceed that figure within the next 30 days.1GOV.UK. How VAT Works: VAT Thresholds Australia’s GST threshold is A$75,000, or A$150,000 for non-profits.2Australian Taxation Office. Registering for GST Canada treats you as an exempt “small supplier” if your revenue stays below C$30,000 across four consecutive calendar quarters, with a C$50,000 figure for charities and public institutions.3Canada Revenue Agency. When to Register for and Start Charging the GST/HST New Zealand sets its threshold at NZ$60,000 over 12 months.4Inland Revenue. Registering for GST
Activities That Force Registration
Some activities require a number no matter how small the business. Importing goods often triggers registration so customs can process the tax. Selling digital services to consumers in another country is another common trigger. Regulated products such as alcohol or tobacco can carry a zero-threshold requirement based on the nature of what is sold rather than the amount.
For digital sales inside the EU, the One-Stop Shop (OSS) lets you register in a single member state and declare the VAT on cross-border consumer sales across the bloc from one portal. An EU-based micro-business can skip OSS entirely if its cross-border B2C digital sales and distance sales of goods stay below €10,000 a year, in which case the sales are taxed in the supplier’s own country.5European Commission. The One Stop Shop Above that figure, the tax follows the customer’s country and OSS becomes the practical way to handle it without registering separately in every member state.
Registering by Choice
You can register voluntarily even if you’re below the mandatory threshold. This tends to make sense when a business spends heavily on taxable inputs, because registration lets you reclaim that input tax. A startup buying equipment and inventory might recover significant VAT/GST before its sales ever hit the compulsory line. The trade-off is that you take on the full compliance load from day one: charging tax on every sale, filing periodic returns, and keeping detailed records.
How to Get a VAT/GST Number
Most tax authorities now register businesses online. In the UK, you apply through the HMRC portal, and you’ll need your company registration number (or National Insurance number if you’re a sole trader), business bank details, your Unique Taxpayer Reference, and figures for current and projected turnover.6GOV.UK. How to Register for VAT In Australia, GST registration is handled through the Australian Business Register at the same time you apply for an Australian Business Number.7Australian Business Register. Applying for an ABN
Timing matters. In the UK, you must register within 30 days of the end of the month in which your turnover passed £90,000.8GOV.UK. Register for VAT Most other countries impose similar windows. Miss the deadline and you owe the tax that should have been collected from the date you were required to register, even though you never charged it to your customers.
What the Number Looks Like
Formats are not standardized globally. Each country designs its own, usually with a country code, a sequence of digits or letters, and a built-in check digit.
Every EU VAT number begins with a two-letter country code identifying the issuing member state.9European Commission. VAT Identification Numbers What follows varies: a German number is “DE” plus nine digits, while a French number is “FR” plus 11 characters that can include letters.10GOV.UK. EU Country Codes, VAT Numbers and Enquiry Letters for EC Sales Lists
Canada builds GST/HST registration into a wider Business Number system. Every business gets a nine-digit BN, and when you register for GST/HST the CRA adds a two-letter program identifier (“RT” for GST/HST) plus a four-digit reference to produce a 15-character account number that links your GST/HST, payroll, and other accounts under one root.11Canada Revenue Agency. Business Number and CRA Program Accounts
Australia’s equivalent is the 11-digit Australian Business Number (ABN) issued by the Australian Business Register, which serves as the core identifier for GST and other government interactions.12ABN Lookup. Format of the ABN India uses a 15-character alphanumeric GSTIN that embeds the state code and the taxpayer’s PAN, which means a single business operating in multiple Indian states holds a separate GSTIN for each one.
Most countries build a mathematical check digit into the number so that a mistyped or transposed character fails validation before a transaction is processed. It’s a simple safeguard that catches a lot of invoicing errors.
Using the Number Day to Day
Once you have a number, it appears on every commercial document you produce, and its role is more than identification.
Invoices
Your registration number must appear on every sales invoice you issue to a registered customer. In B2B transactions, the buyer needs your valid number to claim an input tax credit on the purchase. Cross-border invoices typically need both the supplier’s and the customer’s numbers: the supplier’s identifies who collected the tax, the customer’s confirms their registered status and supports applying a zero rate.
A missing or invalid number is not a formatting issue. Tax authorities routinely deny input tax credit claims when the supporting invoice lacks a valid number, and the buyer absorbs the tax as an unrecoverable cost. Most accounting systems are configured to flag or reject invoices without a valid tax identifier before they enter the ledger.
Cross-Border Sales and the Reverse Charge
When two registered businesses in different countries trade services, many jurisdictions apply a “reverse charge.” Instead of the supplier charging VAT and remitting it in their own country, the customer self-assesses the tax in theirs, reporting both the output tax and the matching input tax deduction on the same return, which usually nets to zero. This removes the need for suppliers to register in every country where they sell services.
For goods moving across borders, the supplier’s registration number supports zero-rating the sale so that the tax falls in the destination country rather than the origin country. The supplier must keep evidence that the goods left the country, including the customer’s verified registration number, to prove the export was genuine.
Checking Someone Else’s Number
Verifying a trading partner’s number before completing a transaction is one of the most practical checks you can run. In the EU, the VAT Information Exchange System (VIES) is a free European Commission tool that confirms in real time whether an EU VAT number is valid, pulling data directly from national databases.13Your Europe. Check a VAT Number (VIES) You can verify any EU member state’s numbers through the portal.14European Commission. VIES VAT Number Validation
Outside the EU, most tax authorities publish their own lookup tools. Australia’s ABN Lookup lets you search any ABN and see whether the entity is registered for GST. A verification takes seconds and can save you from a denied input tax credit or, in the EU, joint liability in a fraud chain.
Filing Obligations After You Register
Getting the number is the start of an ongoing obligation, not a one-time step. You must file periodic returns reporting the output tax you collected and the input tax you paid, then remit the net to the tax authority.
Filing frequency varies by country and by the size of the business. Monthly returns are common for higher-turnover businesses, quarterly filing is the most widespread default, and smaller businesses may qualify for annual filing. Deadlines for submitting the return and paying any balance typically fall within one to two months after the reporting period closes.
Record-keeping goes with the filing. You’ll need to retain invoices issued and received, import and export documentation, and any credit notes or adjustments. Retention periods are commonly five to seven years so the tax authority can audit if questions come up later.
Penalties for Getting It Wrong
The most common failures are registering late, filing late, and issuing invoices with missing or incorrect numbers.
If you should have registered and didn’t, you owe the tax that should have been collected from the date registration was required. HMRC also charges a percentage penalty on top: 5% if you’re up to 9 months late, 10% if you’re 9 to 18 months late, and 15% if you’re more than 18 months late, with a minimum of £50.15GOV.UK. Late VAT Registration Penalty (VAT Notice 700/41) Other countries follow the same pattern: the longer you wait, the worse it gets.
If you accept an invoice bearing an invalid number and claim input tax on it, expect that claim to be denied on audit, and you’ll repay the credit with interest. In the EU, being part of a supply chain where a supplier uses a fraudulent VAT number can expose you to joint liability for the unpaid tax; the test is whether you “knew or had reasonable grounds to suspect” the VAT in the chain would go unpaid.16GOV.UK. Joint and Several Liability for Unpaid VAT (VAT Notice 726) Running a VIES check before a large transaction is cheap insurance against this.
Cancelling a Registration
The number isn’t permanent. In the UK, you can ask to cancel your registration if your taxable turnover falls below £88,000 and you expect it to stay there, and cancellation becomes mandatory within 30 days if you stop trading, sell the business, or change legal structure such as incorporating a sole trade into a limited company.17GOV.UK. Register for VAT: Cancel Your VAT Registration Other countries follow similar logic: if you no longer make taxable supplies, you’re generally expected to deregister.
Cancellation doesn’t end your obligations immediately. You’ll file a final return covering the period up to the cancellation date. In the UK, if you reclaimed VAT on stock or assets you still hold at cancellation and the total VAT on those items exceeds £1,000, that VAT must be accounted for on the final return. Voluntarily registered businesses should weigh this potential clawback before deciding to deregister.