How GST/HST ITCs Work, and Why Not Every Purchase Qualifies

by Kelly O'Toole | Jun 21, 2026 | Canadian Tax Topics

If you’ve ever looked at your GST/HST return and felt a flicker of panic because the amount you owe CRA is nowhere close to what you collected from customers, you’re not alone. A lot of business owners assume GST/HST is a straight pass-through: collect it, send it in, done. When the number on the return doesn’t match that expectation, it’s easy to start second-guessing yourself, wondering if something was filed wrong.

It wasn’t. The GST/HST calculation is a two-part calculation, not a one-part one. The other half is GST/HST Input Tax Credits, or GST/HST ITCs. This is the GST/HST you paid on your own business purchases, and it gets subtracted from what you owe. Once you understand how GST/HST ITCs work, your GST/HST return will finally make sense, and you’ll know what to look for in your own books to make sure you’re not leaving money on the table.

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How GST/HST ITCs Reduce What You Owe

GST/HST ITCs are the GST/HST you paid on purchases for your business. Think of it as the flip side of the GST/HST you charge your customers.

When you file your GST/HST return, you’re not just reporting what you collected. You’re reporting two numbers: the GST/HST you collected on sales, and the GST/HST you paid on your business expenses (your GST/HST ITCs). The difference between those two numbers is what you actually owe to CRA, or what CRA owes back to you, if your ITCs are higher and you get a refund.

$5,000 collected − $1,200 in ITCs =

$3,800 owing to CRA

So if you collected $5,000 in GST/HST from customers and paid $1,200 in GST/HST on business expenses, you don’t owe $5,000. You owe $3,800. That $1,200 is your GST/HST ITCs, and it’s the reason your GST/HST owing is never the same as what you collected.

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Why Don’t the GST/HST ITCs on Every Purchase Qualify

Where this gets confusing is that not every dollar you spend comes with a GST/HST ITC attached.

Some purchases don’t have GST/HST on them at all, things like residential rent, basic groceries, or services from a supplier who isn’t registered for GST/HST. If you did not pay any GST/HST on a purchase, there’s nothing to claim back, no matter how legitimate the expense is.

Personal expenses don’t count either, even if GST/HST was paid on the purchase. The expense has to be for the business.

Documentation matters too. To claim a GST/HST ITC, the receipt or invoice needs to show the supplier’s GST/HST number. If that number isn’t there, CRA can deny the credit, even if you genuinely paid the tax.

This is also where bookkeeping comes in. If a purchase is coded incorrectly in QuickBooks, say it’s marked as “out of scope” or “exempt” when GST/HST was actually paid, that GST/HST ITC gets missed entirely. Multiply that across a year of transactions, and you could be overpaying CRA without realizing it.

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Why the Confusion Sticks Around Even Once You Understand GST/HST ITCs

Even after you understand how collected GST/HST and GST/HST ITCs work together, the actual number on your return can still catch you off guard. That’s usually not a sign you misunderstood the concept. It’s a sign the bookkeeping behind the number needs a closer look.

A few common culprits:

Incorrect sales tax codes on transactions
Missing expense receipts
Duplicate transactions
Incomplete reconciliations
Incorrect opening balances
Prior-period adjustments that affect the cumulative GST/HST balance

Any one of these can shift your GST/HST owing away from what you expected, even when you understand exactly how the math, collected minus GST/HST ITCs, is supposed to work.

Before you file, it’s worth reviewing the bookkeeping records behind the return: confirm your bank accounts, credit cards, and sales are properly reconciled, and that the GST/HST amounts you’re claiming are accurate and supported. The concept is only half the picture. The other half is whether the books feeding into it are accurate.

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What to Check in Your Own Books

A few things worth checking in your own books:

Look at your supplier invoices and confirm that you paid GST/HST and that the supplier’s GST/HST number is on the invoice.
Check how those purchases are coded in QuickBooks. The sales tax code attached to each transaction determines whether that GST/HST gets tracked as a GST/HST ITC, and how much gets recorded.
Don’t wait until filing time to look at this. GST/HST ITCs build up all year in your GST/HST Payable account, and if something’s coded wrong in January, it’s a lot harder to catch by December.

Important: Getting this right matters in both directions. Missing GST/HST ITCs means you’re paying CRA more than you have to, and claiming GST/HST ITCs you’re not entitled to creates a liability if CRA ever reviews your account.

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Conclusion

A GST/HST ITC is simply the GST/HST you paid on business expenses, and it directly reduces what you owe CRA. Once you see your GST/HST return as collected minus GST/HST ITCs, instead of just “what you collected,” the number will make sense, and once your bookkeeping is reconciled and accurate, that number will hold up to scrutiny.

In Short:
Your GST/HST owing is collected minus GST/HST ITCs, not just what you collected. Getting your GST/HST ITCs right isn’t a filing-day task, it’s a year-round bookkeeping habit. The cleaner your coding throughout the year, the more accurate (and often lower) your GST/HST owing will be.