The only rule that matters
Pay off the highest rate first. Every dollar you put against a debt saves you that debt's interest rate, forever, on that dollar. A dollar against a 21.34% card earns you 21.34% a year, guaranteed, tax free, with no risk. A dollar against a 4.24% mortgage earns you 4.24%. So the ranking is the rate column, sorted downwards. Nothing else.
The typical Canadian order in September 2026: credit card 21.34%, cash advance balance 22.99%, unsecured line of credit 7.69%, car loan about 6.50%, HELOC or secured line 4.05% to 5.45%, mortgage 4.24%, federal student loan 0%.
Most households do it backwards
They answer the question by size. The mortgage is the biggest number on the page, so the mortgage feels like the problem, so extra money goes there. Take $10,000 and a household with an $8,000 card at 21.34% and a $420,605 mortgage at 4.24%. Against the card it clears the card entirely and $2,000 goes to the mortgage — and the $1,707 a year the card was costing stops immediately and permanently. Against the mortgage it saves roughly $424 a year, while the card carries on costing $1,707 a year for close to twenty-five years on minimum payments. The card first is better by about $1,280 in the first year alone, and the gap compounds every year the card would have stayed alive.
The 0% student loan
Interest on Canada Student Loans and Canada Apprentice Loans was permanently eliminated on 1 April 2023. A federal student loan at 0% is the last debt any Canadian household should repay early. A household under renewal pressure that is voluntarily overpaying a zero-interest student loan while carrying a 21% card balance is setting money on fire. Note that the federal elimination does not cover Quebec, the Northwest Territories or Nunavut, and most borrowers have a separate provincial portion on separate terms. Check yours specifically.
Where the mortgage fits
Leave it out of this list. It is almost certainly your cheapest debt. Clear the expensive things first, then send what was going to them onto the mortgage — or, better, into your prepayment privilege, which is free and non-cumulative.
The argument for doing it the other way
There is one, and it is not a maths argument. Clearing the smallest balance first gives you a finished account quickly, and for some households that momentum is what makes the plan survive month three. The cost of choosing momentum over rate is usually a few hundred dollars. That is a real cost and it is not an unreasonable price for a plan you will actually stick to.
