The headline figure comes from an example in the Yahoo Finance report: a $500,000 mortgage renewed over a 25-year amortization, with the five-year fixed rate moving from 4.29% to 4.49%. It puts the increase at roughly $55 a month and nearly $3,300 over the term.
The arithmetic holds. Using monthly payments and the semi-annual compounding that applies to Canadian fixed-rate mortgages, the payment rises by $55.29 a month, or $3,318 over 60 payments. But that number measures payments, not cost. The two are different, and the difference runs against the borrower.
A higher rate does two things at once. It raises the payment, and it directs more of each payment to interest. So the borrower at 4.49% pays $3,318 more and still ends the term owing $1,467 more. Added together, that is the $4,785 in extra interest. The $3,300 is the smaller of the two honest numbers.
The effect scales in a straight line with the balance.
These are estimates, not quotes. They assume a 25-year amortization, monthly payments, semi-annual compounding, no prepayments and a rate that moves from 4.29% to 4.49%. A different rate, amortization or payment frequency produces a different result.