A VAT or GST registration number is the unique identifier a national 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 into one account the tax authority can audit. If you sell goods or services in a country with a consumption tax, this number is what lets you legally charge the tax, recover the tax you pay on your own costs, and prove to trading partners that you are a registered business.
“VAT” is the term used across Europe, much of Africa, and parts of Asia. “GST” is the term in Canada, Australia, India, New Zealand, and several others. The mechanics are the same: tax is charged at each stage of the supply chain, each registered business remits the difference between what it collects and what it pays, and the final consumer bears the full cost.
When You Have to Register
Most countries set a sales threshold. Once your turnover crosses it over a defined period, registration becomes mandatory. Stay under the threshold and you are generally exempt from charging the tax, but you also cannot reclaim the tax you pay on your own purchases.
Thresholds differ sharply by country:
- United Kingdom: £90,000 of taxable turnover over the preceding 12 months, or whenever you expect to exceed that figure within the next 30 days.1GOV.UK. How VAT Works: VAT Thresholds
- Australia: A$75,000, or A$150,000 for non-profits.2Australian Taxation Office. Registering for GST
- Canada: C$30,000 over four consecutive calendar quarters marks the “small supplier” cut-off, with C$50,000 for charities and public institutions.3Canada Revenue Agency. When to Register for and Start Charging the GST/HST
- New Zealand: NZ$60,000 over 12 months.4Inland Revenue. Registering for GST
Activities That Force Registration Regardless of Size
Some activities require registration no matter how little you sell. Importing goods into a country with VAT or GST often triggers an obligation so customs can process the import tax. Selling digital services to consumers in foreign jurisdictions is another common trigger. Businesses in heavily regulated sectors like alcohol or tobacco may face a zero-threshold requirement linked to the product rather than the sales volume.
For digital services sold across the EU, the One-Stop Shop (OSS) scheme lets you register in a single member state and declare VAT on all cross-border consumer sales from that 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 Once you cross that figure, the tax shifts to the customer’s country and OSS becomes the practical way to manage it without registering separately in every member state.
Voluntary Registration
You can also register before you hit the threshold. This often makes sense when your business is spending heavily on taxable inputs, since registration lets you reclaim that input tax. A startup buying equipment and inventory may recover significant tax long before its sales reach the mandatory line. The cost is that you take on every compliance obligation from day one: charging tax on every sale, filing returns, and keeping records.
How to Register
Most tax authorities now handle registration online. In the UK, you apply through the HMRC portal and will need your company registration number (or National Insurance number if you are a sole trader), your business bank details, your Unique Taxpayer Reference, and your current and projected turnover figures.6GOV.UK. How to Register for VAT In Australia, GST registration is handled through the Australian Business Register as part of applying for an Australian Business Number.7Australian Business Register. Applying for an ABN
Timing is strict. In the UK, you must register within 30 days of the end of the month in which your turnover crossed £90,000.8GOV.UK. Register for VAT Most other countries use similar windows. Miss the deadline and you will owe the tax that should have been collected from the date you were supposed to be registered, even though you never actually charged it to your customers.
What the Number Looks Like
Formats are not standardized globally. Each country sets its own, usually built around national identifiers, a country code, and a check digit.
Every EU VAT number starts with a two-letter country code identifying the member state that issued it.9European Commission. VAT Identification Numbers After the prefix comes a sequence of digits (and sometimes letters) whose length varies by country. A German number uses “DE” followed by nine digits; a French number uses “FR” followed by 11 characters that may include letters.10GOV.UK. EU Country Codes, VAT Numbers and Enquiry Letters for EC Sales Lists
Canada integrates GST/HST into its wider Business Number system. Every business receives a nine-digit BN, and the CRA adds a two-letter program identifier (“RT” for GST/HST) plus a four-digit reference, producing a 15-character account number that links your GST/HST account to your payroll, corporate income tax, and import/export accounts under one root.11Canada Revenue Agency. Business Number and CRA Program Accounts Australia’s equivalent is the 11-digit Australian Business Number, which doubles as the identifier for GST, income tax, and business reporting.12ABN Lookup. Format of the ABN India uses a 15-character alphanumeric GSTIN whose first two digits are the state code, followed by the taxpayer’s PAN and additional characters covering registration count, business type, and a check digit; a business operating in multiple Indian states holds a different GSTIN in each.
Most countries build a check digit into the number. It is calculated from the preceding characters and exists to catch typos: transpose or mistype a digit on an invoice and the validation fails before the transaction is processed.
Using the Number on Invoices and Cross-Border Sales
Once you have a number, it appears 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 usually need both the supplier’s and the customer’s numbers: the supplier’s identifies who collected the tax, and the customer’s confirms their registered status and justifies applying a zero rate.
A missing or invalid number on an invoice is not merely a formatting issue. Tax authorities routinely deny input tax credit claims when the invoice does not carry a valid number, leaving the buyer to absorb the full tax as an unrecoverable cost. This is why most commercial accounting systems flag or reject invoices with missing tax identifiers before they enter the ledger.
When two registered businesses in different countries trade services, many jurisdictions apply the “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 an output tax and the matching input tax deduction on the same return. The two usually net to zero, and the supplier is spared from registering in every country where it sells services. For exported goods, the supplier’s registration number justifies zero-rating the sale, so the goods are taxed in the destination country. The supplier must keep evidence that the goods actually left the country, including the customer’s verified registration number, to prove the export was genuine.
Verifying Another Business’s Number
Checking that a trading partner’s number is valid before you complete a transaction is one of the most practical due-diligence steps you can take. In the EU, the VAT Information Exchange System (VIES) is a free online tool from the European Commission that confirms whether an EU VAT number is valid, drawing on national VAT databases in real time.13Your Europe. Check a VAT Number (VIES) You can verify a number issued by any EU member state through the portal.14European Commission. VIES VAT Number Validation
Outside the EU, national tax authorities maintain their own lookup tools. Australia’s ABN Lookup lets you search any ABN and see whether the entity is registered for GST. A quick check before processing a large invoice takes seconds and can save you from a denied input tax credit, or from unknowingly being drawn into a fraud chain.
What Comes After You Are Registered
The number is the beginning of an ongoing compliance obligation, not a one-off event. You file periodic returns reporting the tax you collected and the tax you paid, and remit the difference. Filing frequency depends on the country and often on your turnover: monthly for higher-turnover businesses, quarterly as the common default, and annual for smaller operations below certain thresholds. Deadlines for filing and payment usually fall within one to two months after the end of the reporting period.
You will also need to retain the supporting records: invoices issued and received, import and export documentation, credit notes, and any adjustments. Most countries require you to keep these for five to seven years so the tax authority can audit your filings if questions come up.
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 but did not, you owe the tax that should have been collected from the date registration was required. In the UK, HMRC adds a penalty calculated as a percentage of the owed tax, rising with how late you are: 5% up to 9 months, 10% from 9 to 18 months, and 15% beyond 18 months, with a minimum of £50.15GOV.UK. Late VAT Registration Penalty (VAT Notice 700/41) Other countries use different structures, but the pattern is the same: the longer the delay, the steeper the cost.
If you claim input tax on an invoice carrying an invalid or expired number, expect the claim to be denied on audit. You will repay the credit plus interest. In the EU, taking part in a supply chain where a supplier uses a fraudulent VAT number can expose you to joint liability for the unpaid tax even without any intent to defraud; the test is whether you “knew or had reasonable grounds to suspect” that VAT in the chain would go unpaid.16GOV.UK. Joint and Several Liability for Unpaid VAT (VAT Notice 726) That is the practical reason to run a VIES check before processing a large transaction.
Canceling Your Registration
A VAT or GST number is not permanent. In the UK, you can request deregistration if your taxable turnover drops below £88,000 and you expect it to stay there. Deregistration becomes mandatory within 30 days if you stop trading, sell the business, or change legal structure (for example, incorporating from a sole trader into a limited company).17GOV.UK. Register for VAT: Cancel Your VAT Registration Comparable rules apply elsewhere: if you no longer make taxable supplies, you are generally expected to cancel.
Canceling does not clear your slate immediately. You will file a final return covering the period up to your 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, you must account for that VAT on the final return. If you registered voluntarily and are now considering cancellation, factor this potential clawback in before deciding.