Posted: Fri Jul 18, 2008 10:36 am-
Late filing penalties are fixed amounts but I don't know off-hand what they are, I'm sure the CRA will be more than happy to tell you. Then there is a penalty on the amount that you didn't pay as well. I'm sure the rates are on the CRA website, after how you figure out how much back tax you may owe.
There is also the question of how you filed in the US, normally what you should do is file a 1040NR and an 8840 or 8833 to claim the tax treaty exemption. If you filed a 1040 instead then it shouldn't be too big of a problem if all your income was US-source income. Make sure you've filed a 1040-C though otherwise you'll have the IRS after you as well. If you left mid-year you may owe the IRS tax because your personal exemptions will be reduced to the portion of the year you spent in the US. And yippee, if you were filing a 1040 and left mid-year you have to file a dual-status return which means a 1040NR for the portion of the year after you left. And a 1040X to report the change. The more I think about this one you're probably better off phoning the IRS. The main point is though that you cannot retroactively claim a tax treaty exemption, but if all your income in those years was from US sources that doesn't really matter.
The general guide for the T1 explains how to claim a foreign tax credit, however, how you do it retroactively I don't know, you'd have to ask the CRA. Presumably you file for the foreign tax credit with the amended T1.
The general advice I give out on here to anyone resident in Canada who is going to the US temporarily is not to move your tax home to the US unless you're absolutely certain you're going to save enough money on taxes to pay a really accountant to fill all the forms in when you arrive and leave. Unfortunately that doesn't help you at this point.
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Steve.