If you have filed your tax return and realize it has an error, do not file another tax return.

  • Wait for your notice of assessment before making a change.
  • You are allowed to make changes to tax returns in any of the last 10 calendar years.

Make changes online by visiting the Canada Revenue Agency’s My Account website. Make changes by mail by completing Form T1-ADJ (T1 Adjustment Request), or prepare a signed letter that includes the years of the tax return to be corrected, your Social Insurance number, your address and your telephone number. Changes online will take up to two weeks to be corrected, while changes by mail typically take eight weeks.