If you have ever invoiced a customer in Canada and wondered whether you need to charge tax — or a supplier handed you a number you could not make sense of — you are dealing with a GST number. Understanding what it is, when you need one, how to get it, and how to use it correctly can save your business from CRA penalties, denied input tax credits, and costly reassessments. This guide covers everything a Canadian business owner needs to know about GST numbers in 2025.
A GST number is not a standalone identifier. It is a program account attached to your Canada Revenue Agency Business Number (BN). Every business that registers with the CRA receives a 9-digit Business Number — for example, 123456789. When you register for GST/HST, the CRA appends a two-letter program identifier and a four-digit reference number to create your full GST/HST account number:
123456789 RT 0001
The "RT" stands for the GST/HST program. The "0001" is the reference number for your first GST/HST account (businesses with multiple accounts would have 0002, 0003, and so on). When people say "GST number" colloquially, they typically mean the full 15-character account number — the 9-digit BN plus RT 0001 — though sometimes they refer only to the 9-digit BN portion. Either way, both formats are used for verification and invoicing purposes.
Registration is mandatory once your business crosses the small supplier threshold. As of 2025, that threshold remains $30,000 CAD in taxable supplies within a single calendar quarter, or in four consecutive calendar quarters combined. Once you exceed $30,000, you are legally required to register — and to begin collecting GST/HST — from the day you made the supply that pushed you over the limit.
If you earn less than $30,000 per year, you can still register voluntarily. Many small businesses and freelancers choose to do so because registration allows you to claim Input Tax Credits (ITCs) — recovering the GST/HST you pay on business expenses. If you buy significant equipment, software, or materials, voluntary registration often pays for itself quickly.
Registering for a GST number in Canada is straightforward. The CRA provides three methods.
The fastest route is through the CRA's Business Registration Online portal at canada.ca/bro. The process takes approximately 15 minutes and, upon completion, you receive your 9-digit Business Number and RT account number immediately on screen. You will need your Social Insurance Number (if sole proprietor), incorporation number (if incorporated), and basic business information such as your address and fiscal year-end.
You can register by calling the CRA's Business Enquiries line at 1-800-959-5525 (English) or 1-800-959-7775 (French), Monday to Friday during business hours. A CRA agent will walk you through the registration and issue your BN and GST/HST account number by the end of the call.
For those who prefer paper, complete Form RC1 (Request for a Business Number and Certain Program Accounts) and mail it to your tax centre. This method takes several weeks, so it is best avoided if you need to start collecting GST/HST promptly.
Once registered, you must issue invoices that meet CRA requirements. For any taxable sale of $30 or more made to a GST-registered customer, your invoice must include all of the following:
For invoices between $30 and $149.99, slightly simplified requirements apply. For invoices of $150 or more, the buyer's name or trading name must also appear. Getting invoices right matters not just for compliance — it protects your customers' ability to claim ITCs as well.
If you are unsure whether your current invoice template meets CRA standards, the team at Swift Accounting in Calgary can review your bookkeeping setup and ensure your invoicing is fully compliant.
Before claiming an Input Tax Credit based on a supplier invoice, you should confirm that their GST number is valid. The CRA provides a free online tool: the GST/HST Registry, available at canada.ca/gst-hst-registry.
Enter either the 9-digit Business Number or the full 15-character GST/HST account number, along with the date you want to verify for. The registry will confirm whether the number is valid and whether that business was registered for GST/HST on that date. The tool is publicly accessible and does not require a CRA login.
This step is not optional if you want to protect your ITC claims. The CRA can — and does — deny Input Tax Credits if it determines that a supplier's GST number was invalid or that the supplier was not actually registered at the time of the transaction. If a fraudulent supplier gives you a fake number and you do not verify it, you may lose the ITCs and face an assessment for the tax you should have remitted. Routine verification is a simple due-diligence practice that every business purchasing taxable supplies should follow.
Collecting GST/HST when you are not registered is a serious offence under the Excise Tax Act. The CRA can assess you for every dollar you collected and require you to remit it, even if you already spent it. Penalties and interest apply on top. There is no legitimate reason to charge GST without a registration number — if you are approaching the $30,000 threshold, register proactively.
If your revenues exceed $30,000 and you do not register, you become personally liable for all GST/HST that should have been collected and remitted from the moment you crossed the threshold. The CRA can assess back taxes, interest, and late-filing penalties going back several years. In cases of gross negligence, additional penalties of 25% of the unpaid tax can apply. If you are uncertain whether you have crossed the threshold, Swift Accounting Calgary can help you review your revenue history and determine your obligations.
Your Business Number (BN) is the 9-digit identifier assigned to your business by the CRA. A GST number — more precisely, a GST/HST account number — is that same 9-digit BN with RT 0001 appended. The BN is the root identifier; the RT account is one of several program accounts (others include payroll, corporate income tax, and import/export) that can be attached to it.
No. Your federal GST/HST number is valid across Canada. However, if you do business in Quebec, note that Quebec administers its own provincial tax (QST) separately through Revenu Quebec, and you may need a separate QST registration. For HST provinces (Ontario, Nova Scotia, New Brunswick, Prince Edward Island, and Newfoundland and Labrador), your single federal GST/HST registration covers both the federal and provincial portions — there is no separate provincial registration needed.
If you register online through the CRA's Business Registration Online portal at canada.ca/bro, you receive your Business Number and GST/HST account number immediately upon completing the application — typically within 15 minutes. Phone registration is similarly fast. Mailing Form RC1 can take several weeks, so online registration is strongly recommended whenever time matters.
Yes, within limits. You can request an effective registration date up to 30 days before the date you submit your application. If you discover you should have registered earlier because you crossed the $30,000 threshold months or years ago, you should contact the CRA proactively. Voluntary disclosure can reduce penalties and interest in many circumstances, but you will still owe the tax that should have been collected and remitted.
GST/HST compliance is one of those areas where a small mistake — missing the registration deadline, issuing non-compliant invoices, or failing to verify a supplier's number — can trigger a CRA audit and a significant tax bill. Whether you are registering for the first time, cleaning up past filings, or just want a second set of eyes on your processes, professional guidance pays for itself.
Contact Swift Accounting today to speak with a Calgary accountant about your GST/HST obligations, registration, or filing strategy. We work with small businesses, incorporated companies, and self-employed individuals across Alberta and beyond.
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