Canadians can generally receive a non-refundable tax credit for charitable donations up to 75% of their net income (i.e. income minus deductions). I wrote a long post last month on the calculation of Canadian income tax, and in this post I mentioned that, for couples filing jointly, charitable donations should be pooled onto a single tax return.
The reason for this is that the first $200 of donations that you claim generate a credit at the lowest marginal tax rate (21.05% in Ontario for 2007), while anything over $200 is credited at the highest rate (40.16% in Ontario for 2007). If a husband and wife each donated $300 to an eligible charity this year, and claimed the donations individually, then each person would receive a 21.05% credit on the first $200, and a 40.16% credit on the last $100, for a total credit of $42.10 + $40.16 = $82.26 each. If, on the other hand, the entire $600 were claimed on a single return, then the the total credit would be $42.10 + $160.64 = $202.74, or $101.37 each. That's $38.22 in extra tax savings for the couple, just for claiming the donations jointly.
Until recently, I was under the impression that it doesn't matter which return you claim the taxes on, provided both returns have taxes against which to apply the credit. However, as I discovered while going over our own taxes last week, it does make a difference. The main reason for this is the provincial surtax, which is added if your provincial taxes owing are over a certain amount. In Ontario, for 2007, the surtax is 20% on taxes between $4,101.01 and $5,172, and 56% on taxes over $5,172. Because the surtax is calculated after applying any credits, the benefit of a tax credit is greater for taxpayers in higher provincial income brackets.
If your Ontario taxes (before credits and surtax) come to $4,000, then a $1 provincial credit saves you $1 in taxes, since you are below the surtax limit. However, at $5,000, your $1 credit saves you $1.20, and at $6,000, it saves you $1.56. For the $600 donation example above, the $202.74 credit is made up of $146.00 federal and $56.74 provincial. This means that someone with $4,000 in provincial taxes would save $56.74, while someone paying $6,000 would save $88.51. Clearly, it makes sense for the donations to be claimed by the person with higher total taxes.
By claiming our $1,300 in 2007 donations on my own return instead of Ms. Loonie's return, we end up saving an extra $75 in taxes as a couple. That's $75 that we can divvy up between us however we want.
Who are we to turn down free money?