Backdating HST Registrations: What to Do If You’re Late Getting an HST Number

It is quite common for a Canadian business owner to be caught off guard by the rules around GST/HST registration.

Whether you run a consulting business, a construction company, or an e-commerce shop, there’s a point when you are legally required to register and start charging HST to your clients.

Missing that deadline can mean trouble. If you delay registering and the CRA backdates your HST number, you could end up owing thousands in uncollected taxes even if you never charged HST to your customers.

Here’s why this happens, why it’s easy to miss, and what you can do if you’re late in getting an HST number.

When Do You Need to Register for HST?

In Canada, businesses must register for GST/HST once they are no longer considered a small supplier.

• A small supplier is someone who earns $30,000 or less in worldwide taxable revenues in a 12-month period.
• Once you cross the $30,000 threshold, you must register for HST and start charging it on your sales.
• Certain businesses (like ride-share drivers and taxi operators) must register right away, no matter how small their revenue.

Many entrepreneurs don’t realize that the CRA expects you to start charging HST from the moment you exceed that $30,000 threshold.

What Happens If You Register Late?

If you only realize months (or years) later that you should have registered earlier, the CRA can backdate your registration.

This means:

• You’ll be liable for HST on all taxable sales going back to your effective registration date.
• You will have to pay HST to the CRA, even if you never charged it to your customers.
• You may also face penalties and interest on the unpaid amounts.

Example:

Imagine a consultant who earned $45,000 in taxable revenue in 2023 but only registered for HST in 2025. The CRA can backdate his/her registration to the point in 2023 when they crossed $30,000. That consultant may now owe HST on all sales from that date forward tens of thousands of dollars they never collected if HST was not charged to their customers.

Why Is This Easy to Miss?

There are several reasons business owners miss the HST registration deadline:

• Confusion about the small supplier threshold. Many think $30,000 applies per calendar year instead of a rolling 12-month period
• Rapid growth. A side hustle can suddenly take off, pushing revenue above the threshold before you realize it
• E-commerce complexities. Selling online across provinces (or internationally) can make HST rules even harder to track

Penalties and Consequences of Backdating

The consequences of late registration can be serious:

• Uncollected HST liability. You may have to pay HST out of your own pocket if you didn’t charge HST to your clients
• Penalties and interest. CRA can charge late filing penalties and interest on unpaid amounts
• Input tax credit limitations. You may lose the ability to claim ITCs (HST you paid on business expenses) for periods before your official registration date
• Cash flow strain. Having to suddenly remit large amounts of uncollected HST can cripple cash flow for a small business

Here is a Checklist of What To Do If You’re Late Getting an HST Number

If you realize you should have registered earlier, don’t ignore it. Here are the steps to take:

1) Confirm the effective registration date you should have had

• Work out the exact date you ceased to be a “small supplier” (the day your rolling 12-month taxable revenues went over $30,000) or another date that triggers mandatory registration. This date is the effective date the CRA will use when backdating.

2) Gather the documents CRA will want

Collect robust evidence for the period you want backdated (and for a few months either side).

Typical items CRA requests include:

• Copies of sales invoices showing HST was charged (if you charged it). If you didn’t charge HST, invoices still help show when supplies were made.
• Sales journal / POS reports summarizing daily/weekly sales.
• Bank statements showing deposits from customers (matches sales).
• Contracts, estimates, work orders or signed proposals with dates.
• Expense invoices / receipts (to calculate ITCs).
• Any correspondence or notices confirming timing.

3) Decide whether you’ll ask CRA to backdate or do a voluntary disclosure

• If the CRA has not contacted you: request backdating or use the VDP.
• If the CRA has contacted you: disclosure will usually be “prompted” with reduced relief.

4) If you want the registration backdated: prepare a clear request package

• Write a short cover letter explaining:

1. The factual timeline
2. The effective date requested
3. Supporting documents included

• Include at least 5–6 invoices around the backdate period.

5) Expect CRA’s practical limits

• Automatic 30-day backdating is common.
• Longer backdates require stronger proof.

6) Calculate what you owe

• Prepare draft backdated GST/HST returns:
  • Total taxable supplies (HST collectible)
  • Input Tax Credits (ITCs)

7) File the backdated GST/HST returns

• If CRA approves the backdate, file all required returns.
• If using VDP, include backdated returns in the application.

8) Be ready to pay

• HST owing + possible penalties & interest.
• Payment arrangements may be available.

9) Fix accounting and customer communications going forward

• Ensure your system charges HST correctly.
• Consider whether retroactive invoicing is feasible.

Final Thoughts

Backdating HST registration is one of the most common—and costly—compliance issues for Canadian small businesses. The rules are easy to misunderstand, and missing the registration deadline can saddle you with a large, unexpected tax bill.

The good news is that the problem can be fixed. By acting quickly, registering properly, and using the Voluntary Disclosures Program if necessary, you can bring your business into compliance and protect your cash flow.

If you’re late registering for HST, contact TaxHelp.ca today for help getting back on track before CRA penalties pile up.