How far back can you claim missed deductions?
The CRA windows for recovering a credit or deduction you missed in a past year, by how you file.
Published June 18, 2026 · 5 min read
If you missed a deduction or credit in a past year, you can often still recover it by amending the return. How far back you can go depends on how you file. Corporations have about three years from the notice of assessment. Individuals can usually go back up to ten. SR&ED has a hard 18-month cutoff with no discretion. GST/HST input tax credits run about four years. Grants are the exception: they are forward-looking and cannot be claimed for a year that has passed. Confirm the eligible years with your accountant before you file anything.
Corporations: about three years
For a corporation, the normal reassessment period is roughly three years from the date on the notice of assessment, a little longer for some larger corporations. Inside that window you can file an amended T2 or a written adjustment request to claim a deduction or credit you missed. After it closes the year is generally statute-barred, meaning the CRA will not reopen it except in narrow circumstances.
Individuals: up to ten years
Sole proprietors and partners file personally, and the CRA accepts change requests on a personal return for up to the ten previous calendar years. The first three years are routine; beyond that the CRA has discretion under the taxpayer relief provisions. You make the request with a T1 adjustment, using the T1-ADJ form or ReFILE through your software or CRA My Account.
SR&ED: a hard 18-month window
SR&ED is the strict one. The claim must be filed within 18 months of your fiscal year-end, on Form T661. There is no discretion and no extension: miss the date and the credit is lost, even though the underlying research was real. If you have done R&D and not claimed it, check this date before anything else.
GST/HST input tax credits: about four years
If you paid GST or HST on business expenses and did not claim the input tax credit, you can generally recover it within about four years by adjusting a past GST/HST return. Most small businesses have a longer window here than they expect.
Grants cannot be claimed retroactively
Grants and most incentives are applied for before or during the project, on the program's schedule. There is no mechanism to claim a grant for a year that has already gone by. This is why the recovery story is really about credits and deductions, the things claimed on a return.
How to actually file the change
For a personal return, use ReFILE or a T1 adjustment. For a corporation, file an amended T2 or send an adjustment request with the corrected schedule. For SR&ED, file Form T661 within the window. In every case, keep the documents that support the claim, and confirm the eligible years with your accountant, because the exact window depends on your facts.
Deductly flags, for every deduction and credit it surfaces, whether a missed year can still be recovered and roughly how far back, so you are not leaving recoverable money in closed years. Run the quiz to see which of your matches are recoverable.