Changing your tax return once you have already filed itIncome Tax Act S. 142(4.2)
If you have filed your return and then determine that you need to make a change, either because you have received another T-slip, or because you didn't claim an expense and later learned it was deductible, you can request an adjustment to your tax return.If you've just discovered that pension splitting with your spouse would save you some tax, this is also a good reason to adjust your prior return. However, make sure that combined taxes payable are reduced by doing this, and keep in mind that the taxes payable of one spouse will probably increase, resulting in interest on the tax amount payable.The time limit for filing adjustments to your tax returns by mail is ten (10) years. An adjustment request may be made in 2013 for the 2003 or subsequent taxation years.You can request the changeonline for your most recent return, or your returns for the previous two tax years, orby mail, for tax returns for the past ten years.Requesting a change onlineRequesting a change online is very simple, and is done by logging into your account at the CRA My Account page. A separate request has to be filed for each tax year.You can also use the online request if you forgot to apply for the GST/HST tax credit when you filed your tax return.Requesting a change by mailYou can obtain a form T1Adj from the CRA web site, complete it and mail it in, along with documents supporting your change request.See also the CRA web page How to change your return.