How far back can you fix a Canadian tax return?

The rule, precisely

Section 152(4.2) of the Income Tax Act lets an individual ask the CRA to reassess a tax year after the normal reassessment period has closed, as long as the request is made on or before the day that is 10 calendar years after the end of that year. Section 164(1.5)(a) is what allows a refund to actually be paid out on such a request.

Two limits matter more than most people expect. First, this is discretionary relief, not an entitlement — the CRA can decline. Second, the window is measured in calendar years, not rolling months: it moves every January 1, and when a year drops off it is gone permanently. There is no late application.

Which tax years are still open right now

A request made today reaches the 10 tax years below. Each deadline is December 31 of the tenth year after the tax year ends.

Closing next. 2016 stops being reachable after December 31, 2026. After that date, no adjustment to 2016 can produce a refund, regardless of what was missed.

Three channels, three different reaches

“ReFILE” is often used loosely to mean any amendment, but it is one specific CRA service with the shortest reach of the three. Picking the wrong channel is the most common reason people conclude a year is closed when it isn't.

Change my return (CRA My Account)

The 10 most recent tax years

The online form inside My Account. This is the channel that actually delivers the full 10-year reach. It is blocked for some situations — bankruptcy years, a deceased taxpayer's optional returns, and multi-jurisdiction (T2203) years — and it cannot be used to make or revise an election.

ReFILE (through certified tax software)

A rolling handful of recent years only

Submitted through NETFILE- or EFILE-certified software, so it suits a year you filed electronically and want to correct quickly. Its year range is a rolling window that moves each filing season, and it is materially shorter than 10 years. Confirm the accepted years inside your software at the time you file.

Form T1-ADJ, by mail

Any year — but no refund past 10 years

The paper fallback. It reaches any year and handles the special situations the online channels refuse. The catch is on the money, not the filing: a refund cannot be issued for an adjustment requested more than 10 calendar years after the end of the tax year.

The deadlines that are shorter than 10 years

The 10-year window governs asking for a reassessment. Several specific items have their own, tighter clocks that expire first — and in some cases cannot be extended at all.

• Pension income splitting — 3 years

  A late, amended, or revoked T1032 election must be made within three calendar years of the filing due date for that year. Both spouses have to agree. This one expires long before the 10-year window and is among the most commonly missed.

• Topping up a permissive deduction — not allowed at all

  If you deliberately claimed less capital cost allowance (or another permissive deduction) than you were entitled to, the CRA will not process a later adjustment whose only effect is to increase it.

• Corporate dividend refund — 3 years, absolute

  The return generating the refund must have been filed within three years of the end of the tax year. The Tax Court has confirmed this bar is absolute: no waiver, no taxpayer relief.

• SR&ED claims — about 18 months

  The T661 and Schedule 31 are due 12 months after the return's filing due date, roughly 18 months after year end. The CRA has no discretion to extend this.

If you are incorporated, this rule is not yours

This is worth being blunt about, because “10-year lookback” gets marketed broadly and it is simply not available to a corporation. Section 152(4.2) covers individuals other than trusts and graduated rate estates. A corporation instead gets the normal reassessment period: generally three years for a Canadian-controlled private corporation, four for other corporations, running from the day the original notice of assessment was sent — not from the year end, and not from any later reassessment.

Past that period, a downward corporate reassessment is exceptional: it needs a waiver filed in time, a carryback consequence, a misrepresentation, or a court or objection outcome. If you own a corporation, the practical takeaway is that your personal return may still have a decade of room while your corporation has far less — and the corporate clock is the one to check first.

Quebec files twice

Quebec administers its own personal income tax. A federal adjustment does not amend your Quebec return — you file a separate request with Revenu Québec, on Form TP-1.R-V. If you are a Quebec resident correcting a past year, budget for both.

An honest caveat. Revenu Québec's administrative guidance describes a lookback covering tax years ending in the ten civil years before the request, which would mirror the federal window. We have not been able to confirm that against primary source text — Quebec's Tax Administration Act sets a four-year assessment period, and we found no statutory equivalent to the federal 10-year mechanism. Treat the 10-year figure for Quebec as administrative practice and confirm it with Revenu Québec before relying on an older year. We would rather flag the gap than repeat a number we cannot trace.

How long it takes

Anything reaching past the normal three-year period counts as a complex adjustment, as do multi-year requests, carrybacks, pension-split changes, and bankruptcy or deceased returns. The CRA's published service standard for those runs to 45–49 weeks, and the Taxpayers' Ombudsperson observed cases reaching 47 weeks in June 2026. Plan around close to a year, and file well before a December 31 cliff rather than into it.

Questions