Why a Canadian mortgage does this at all
A Canadian mortgage has an amortization, which is how long until it is paid off, usually 25 years, and a term, which is how long the current contract lasts, usually five years or less. At the end of the term the loan does not end. It is renewed at whatever rates exist that week. That is why a rate move reaches every Canadian borrower on a schedule, a cohort at a time, whether or not they moved house, refinanced or did anything at all.
The semi-annual thing, and why it matters here
Canadian fixed-rate mortgages compound semi-annually, not in advance. The monthly rate is the sixth root of one plus half the annual rate, minus one. At 2.20% that is a monthly factor of about 0.001824, not 0.001833. On a $500,000 mortgage the difference between the two methods is a couple of dollars a month, which sounds trivial until it compounds over 300 payments and changes your balance at renewal. Variable-rate mortgages compound monthly, so this calculator switches method when you tell it the new rate is variable.
What the book's worked household looks like
They borrowed $500,000 in September 2021 on a five-year fixed at 2.20% over 25 years. The payment was $2,166. After 60 payments the balance was $420,605. Renewing at 4.24% over the 20 years left gives $2,594 — an increase of $428 a month, or 19.8%. That cross-checks against the Bank of Canada's "about 20%" for five-year fixed renewals in 2026, which is reassuring, because it means the example is not an outlier chosen to frighten anyone.
Scaling it, roughly
The increase scales roughly with the balance. Going from 2.20% to 4.24% over 20 years is about +$205 a month on $200,000, +$305 on $300,000, +$428 on $420,000, +$610 on $600,000 and +$815 on $800,000. Those are for orientation only. Use your own remaining amortization, because it changes the answer as much as the balance does.
Then make the number smaller
In rough order of how much they are worth: get a better rate (worth $50 to $400 a month), extend the amortization (a real lever with a large, knowable price), clear expensive debt elsewhere (often the biggest number in the household), and ask your lender for relief if you are genuinely in difficulty. Do them in that order, and do the first one before you sign anything.
