How do I correct a GST/HST return I already filed?

Small errors: fix them in the next return

If you find a minor error, such as a missed input tax credit or a small over-reported amount, the simplest fix is often to adjust it in your next GST/HST return. You would include the correction in the appropriate line of the following period rather than reopening the filed one.

This works for input tax credits in particular, because you generally have up to four years to claim a credit you were entitled to. Missing an ITC on one return does not mean it is lost; you claim it later within the window.

Formal adjustments through My Business Account

For larger corrections, errors affecting a period you cannot easily net against, or changes to previously reported sales, you request an adjustment. The cleanest route is CRA My Business Account, which lets you adjust a filed return online. You can also write to your tax centre with the reporting period, the lines affected, the corrected figures, and an explanation.

Keep the supporting documentation. An adjustment that increases your refund or reduces tax owing is more likely to draw a review, so the paperwork behind it should be ready before you file the request.

If you under-reported and owe more

Where the error means you collected more tax than you remitted, correct it promptly. Interest accrues on unremitted GST/HST from the original due date, and because this is trust money the CRA treats shortfalls seriously.

Coming forward before the CRA finds the error is always better than waiting. If the amount is significant and more than a year overdue, the Voluntary Disclosures Program may reduce penalties and part of the interest, but only if you disclose before the CRA contacts you about it.

Common errors worth checking for

• Claiming ITCs on expenses that are only partly commercial, or on the 50% non-deductible portion of meals
• Charging the wrong provincial rate under the place-of-supply rules
• Missing ITCs on large capital purchases or startup costs
• Treating a zero-rated or exempt supply as taxable, or the reverse
• Quick Method filers claiming ITCs they have already given up by electing the method

Several of these recur every period, so fixing the process matters as much as fixing the single return.

When to just call it a wash

Not every tiny discrepancy needs a formal adjustment. The CRA does not expect perfection to the dollar, and immaterial differences that net out over adjacent periods are generally acceptable to correct in the ordinary course. Reserve formal adjustment requests for material amounts, closed periods, or corrections that change your refund position meaningfully.