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To correct accounting errors from a previous period in Canada, you fix the books first and then change whichever filed return the error touched. Personal returns, corporate returns and GST/HST returns each have their own way to do that, and none of them involves filing the old return again.
What comes first when you correct accounting errors?
The books. A return is only a summary of them, so if the ledger still holds the wrong number, every later return inherits it. Post the correction, write a short note on what was wrong and why, and keep the supporting documents with it. That note is what you’ll hand over if the CRA asks.
A good note is short: the date, the period affected, the old amount, the new amount and the document that proves it. Two lines is fine.
How a correction shows up in your financial statements is a separate question from how it shows up on a tax return. The financial reporting rules weren’t confirmed on an official page, so a corporation with statements that an accountant signs off on should ask that accountant how the prior period gets restated.
In what order do you fix things?
- Find the error and work out which periods it touched.
- Correct the books and write the note.
- List every filed return that used the wrong number: income tax, GST/HST, payroll slips.
- Use the right route for each one, from the table below.
- Keep copies, then watch for the notice that confirms the change.
Skipping step three is the usual slip. One wrong sale can sit in an income tax return and a GST/HST return at the same time.
How do you change a return you already filed?
| Return | How the CRA says to correct it |
|---|---|
| Personal (T1) | Change my return in your CRA account, or ReFILE in certified software, or form T1-ADJ by mail. Online runs about 2 weeks, mail about 19 |
| Corporation (T2) | Request a reassessment, fastest through current tax software, or by letter to the tax centre with the business number, tax year and revised statements or GIFI |
| GST/HST | Use Adjust a return in My Business Account, or write to your tax centre. Don’t file a new return |
| Payroll slips (T4) | Send an amended slip. The CRA says there is generally no time limit to amend T4 slips |
For a personal return, you wait for your notice of assessment first. A refund can’t be issued for a change that reaches back more than 10 calendar years, according to the CRA’s page on changing your return. On paper, you attach support for the whole amount, including amounts you claimed before but never documented.
For a corporation, send revised schedules and statements, not a second copy of the full T2. For payroll slips, the CRA’s page on correcting deduction errors covers the steps.
Three quick pictures. A freelancer who under-reported income uses Change my return. A shop owner who claimed too much HST uses Adjust a return in My Business Account. An employer who issued a wrong T4 sends an amended slip. Different doors, same idea.
What does a mistake cost in real money?
Take a sole proprietor in Ontario who reported $60,000 of net business income when it should have been $68,000. The self-employed tax calculator puts income tax plus CPP at $14,602.92 on $60,000 and $17,527.40 on $68,000. The $8,000 slip is worth $2,924.48 in tax and contributions, about 37 cents on the dollar.
That figure leaves out interest and any penalty, which depend on the dates and on what the CRA decides. The calculator also ignores business expenses and, by its own note, EI and GST/HST. For a company, the corporate tax calculator gives a rough feel for the swing, and the income tax calculator does the same for an employee whose slip was wrong.
When should you use the Voluntary Disclosures Program?
If the error means tax went unpaid and penalties or interest may apply, the program is worth a look. On the CRA’s current terms, an application you make on your own before the CRA contacts you normally gets 75% relief of interest and 100% relief of penalties. If the CRA has already made contact, that drops to 25% of interest and up to 100% of penalties.
You still pay the tax. The application must be voluntary and complete, and you have to pay or arrange payment of the estimated amount owing. GST/HST disclosures follow one CRA memorandum and income tax follows another, so use the right one. Applications received on or after 1 October 2025 fall under the newer GST/HST memorandum.
An error that cost you money, like a missed expense, doesn’t need this at all. You just change the return and wait for the refund. Simple.
Mistakes that make the fix harder
The big one is filing a fresh return for the old period. Don’t. For GST/HST the CRA says so in plain words. Another is patching it inside the current year’s books without telling anyone, which buries the error and creates a second one. And a correction that never reaches the return leaves the CRA holding the old number.
The sources behind this page
The processing times, the 10 year limit and the T1-ADJ steps come from the Canada Revenue Agency‘s page on changing a return. T2, GST/HST and T4 steps come from CRA pages on corporation reassessments, filing a GST/HST return and amending slips. The relief percentages come from the CRA’s Voluntary Disclosures Program pages, checked in September 2026. The dollar example comes from our calculator and uses our 2026 tax data.
Frequently asked questions
Do I file a new return to fix an old one?
No. For GST/HST the CRA says don't file a new return. Use the adjustment options, such as Adjust a return, or write to your tax centre.
How far back can I change a personal tax return?
The CRA says a refund can't be issued for an adjustment request beyond 10 calendar years. You need your notice of assessment first.
Is there a time limit to amend a T4 slip?
The CRA says generally there is no time limit to amend T4 slips.
Can I avoid penalties by coming forward?
Possibly. An unprompted Voluntary Disclosures Program application normally gets 75% interest relief and 100% penalty relief, but you still pay the tax.
Does the CRA have separate rules for restating financial statements?
Tax returns and financial statements follow different rules. We didn't confirm the reporting rules on an official page, so ask your accountant.
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