For the many couples, it won't matter. The actual tax savings federally and provincially is the same regardless of income. There are two situations where it can make a difference. One is, if the lower income spouse does not need all of the credits to reduce their tax liability to zero. Also, in Ontario, on the provincial tax form, if your tax liability is high enough, you get to pay tax on the tax (surtax). In both the situations I mentioned, it is definitely better for the donations to be reported on the higher income spouse.