Who can file Form T1-ADJ?
An individual who has already filed a Canadian return and needs it changed, where the year is still inside the reassessment window. That covers adding a credit that was missed, correcting income that was reported wrongly, and fixing a computation that went wrong because of residency, such as a part-year calculation or income taxed as though the filer had been resident for the whole year. The common thread is that the return exists and its figures need to be different. Where no return was ever filed there is nothing to adjust, and the year needs the return itself.
How far back can I change a return I already filed?
As far back as the reassessment window for that year allows, and no further. So the first task on a file with several problem years is to date each year and sort them into those still inside the window and those outside it, because the two groups need different handling and the reachable years should not be allowed to age out while paperwork is assembled. Filing an adjustment for a year that has closed is worse than wasted effort. It is usually the reason a client believes their position has been considered when in fact it has not.
Can I use Form T1-ADJ to report foreign income I left off?
This is the question to settle before anything is filed. An adjustment is the right tool for an error and the wrong tool for unreported foreign income: a disclosure application preserves relief that an ordinary adjustment does not, and once the income has arrived by way of a plain adjustment that relief may no longer be available. The difference has nothing to do with the amount involved. It is about which route you enter by, and the route is chosen before the first document goes in, not after the agency writes back.
Can I file an adjustment if I never filed the return?
No. The form adjusts a return that has been filed, and an unfiled year has nothing to adjust. This comes up more often than it sounds, because a client with a run of problem years frequently has some filed and some not, and the pile looks identical from the outside. The unfiled years need returns. The filed ones may need adjustments. Separating the two is the first job on that kind of file, and it changes both the order of work and what the real exposure on each year is.
Can a non-resident use Form T1-ADJ to fix a residency computation?
An adjustment is the route where the return was filed and the residency-driven computation inside it came out wrong, such as a part-year return prepared on the wrong dates, or income included for a period when the filer was not resident. That is a correction to your own figures. It is a different thing from disagreeing with the agency's view of your residency: where the agency has assessed a residency position you dispute, that is a dispute about the assessment, with its own deadline, and an adjustment request cannot carry it.
Do I file an adjustment or a formal objection?
It depends on whose figures are wrong. An adjustment asks for a correction to what you filed: a credit you omitted, income you reported incorrectly, a computation you got wrong. An objection disputes what the agency assessed, and it runs on a deadline measured from the notice rather than on the reassessment window. If the assessment simply reflects the return you filed, there is nothing in it to dispute and the adjustment is the route. If the agency changed your figures and you disagree with the change, the adjustment is not the route.
Is double taxation illegal?
It is legal. Two countries can each have a valid claim on the same income — one because the income arose there, the other because you live there — and nothing prohibits both from exercising it. What exists instead is relief: tax treaties allocate the claim, and domestic law gives a credit for foreign tax paid. The relief is not automatic, though. It is claimed on a return, and unclaimed relief is simply lost. See how double taxation is relieved.
Is double taxation legal?
Yes. Nothing prevents two countries from taxing the same income under their own domestic law — each is exercising its own jurisdiction. What treaties and credit systems do is relieve the outcome rather than prohibit the charge, and relief is generally something you must claim on a return or a form, not something applied automatically. Miss the claim and the double charge stands. Double taxation explains the mechanism.
