Thirteen tax systems on one federal base
Every province and territory except Quebec has its income tax collected by the CRA on the same T1 return, using its own brackets, credit rate and basic personal amount. Ontario’s surtax and Health Premium, British Columbia’s tax reduction and Alberta’s supplemental credit all come from the province’s own rules file. Quebec residents file a separate TP-1 return with Revenu Québec, which is why Quebec has its own rules file here.
Pay frequency and the mid-year edition
Most Canadian employers pay bi-weekly (26 pays) or semi-monthly (24). The CRA publishes payroll formulas (T4127) in January and, when rates change, again in July, so withholding can shift halfway through the year. The calculator works on the full-year rules used for your return, so it shows the tax you actually owe rather than the amount withheld in a particular month.
When CPP and EI stop
Because CPP, CPP2 and EI have annual maximums, higher earners see their paycheques rise once the year’s contributions are complete — often in the autumn. The annual figures here already include the cap; a single month’s payslip may show more or less.
Credits beyond the basics
Tuition, medical expenses, charitable donations, the disability amount and spousal credits all reduce tax but depend on your circumstances, so they are left out. If you claim them on your TD1, your withholding will be lower than this calculator suggests, and the refund on your return smaller.