How Mortgages Work in Canada: Down Payments, Rates, and Amortization Explained

Most explanations of Canadian mortgages jump straight to rates — but the rate is only one of several numbers that actually determine what you can borrow and what you'll pay. Down payment tiers, mortgage insurance, the stress test, and amortization all interact, and missing any one of them is how buyers get surprised partway through the process.

The minimum down payment, by price tier

Canada's minimum down payment isn't a single percentage — it scales with the purchase price:

Why the down payment tier matters: mortgage insurance

Any mortgage with less than 20% down is a high-ratio mortgage, and by law it must be insured — through CMHC, Sagen, or Canada Guaranty. The insurance premium (a percentage of the loan amount, usually added directly to the mortgage principal rather than paid upfront) protects the lender, not the borrower, if the loan defaults.

Putting down 20% or more makes it a conventional mortgage, which doesn't require this insurance — one of the real financial advantages of reaching the 20% threshold, beyond simply having a smaller loan.

Amortization: 25 years is the default, not a rule

Amortization is the total time it will take to pay off the entire mortgage. For an insured (high-ratio) mortgage, the maximum amortization is 25 years — though first-time buyers and buyers of newly constructed homes may qualify for 30-year amortization on insured mortgages, which lowers the monthly payment but increases total interest paid over the life of the loan.

Amortization is different from your term — the length of time your current rate is locked in, typically 1 to 5 years. You renegotiate a new rate at every term renewal, but the amortization clock (the total payoff timeline) keeps counting down across however many terms it takes.

The stress test: why your approved amount isn't based on your actual rate

Federally regulated lenders are required to qualify every buyer at the higher of two numbers, under OSFI's Guideline B-20:

• Your actual contract rate plus 2 percentage points, or
• 5.25% (the current minimum qualifying rate).

As of November 2024, one exemption applies: a straight switch between lenders at renewal — with no increase to the loan amount or amortization — doesn't require re-qualifying under the stress test. This exemption affects an estimated 70% of mortgages at renewal, making it meaningfully easier to shop for a better rate without requalifying from scratch.

GDS and TDS: the two ratios that actually cap your borrowing

Lenders calculate two debt-service ratios against your gross income, and whichever is tighter sets your real limit:

• GDS (Gross Debt Service), capped at 39%: mortgage payment, property tax, heating costs, and half of condo fees (if applicable), divided by gross income.
• TDS (Total Debt Service), capped at 44%: everything in GDS, plus all other debt payments — car loans, credit cards, lines of credit — divided by gross income.

A buyer with no other debt might max out GDS before TDS becomes relevant. A buyer carrying a car loan and credit card balances often finds TDS is the binding constraint, reducing how much mortgage they actually qualify for even if GDS alone would allow more.

A worked example

Priya and Dev are buying a $650,000 home with 10% down ($65,000), leaving a $585,000 mortgage, which requires insurance since it's a high-ratio mortgage. Their lender quotes a 4.75% rate on a 5-year term, 25-year amortization.

• Stress test qualifying rate: the higher of 4.75% + 2 = 6.75%, or 5.25% → they're qualified at 6.75%.
• Their actual monthly payment is calculated at 4.75%, but their approved borrowing amount was limited by what they could afford at 6.75%.
• At the end of their 5-year term, they'll need to renew — either with their current lender or by switching, and if they switch without increasing the loan or amortization, they won't need to pass the stress test again under the current exemption.

Why mortgage renewal is a bigger deal than usual right now

Mortgage renewal isn't automatic approval of whatever your lender offers — it's a negotiation point, and increasingly, a shopping decision. Comparing your lender's renewal offer against other lenders before signing is one of the few places in a mortgage's lifecycle where a borrower has real leverage.

Common mistakes

• Confusing the stress-test rate with the actual payment rate. The stress test determines what you qualify to borrow, not what you actually pay — the two numbers are routinely very different.
• Treating 25-year amortization as fixed. First-time buyers and new-build buyers may be eligible for 30-year amortization on an insured mortgage, which meaningfully changes monthly affordability.
• Assuming 20% down avoids all extra cost. It avoids mortgage insurance specifically — it doesn't exempt a buyer from the stress test, which still applies to conventional mortgages.
• Accepting a renewal offer without shopping it. With such a large renewal cohort in 2025-2026, lenders are competing harder for renewal business than is often assumed — a straight switch (no increase to loan or amortization) usually doesn't require requalifying.
• Forgetting TDS when other debt exists. A strong income doesn't guarantee the expected mortgage amount if car loans or credit card balances push the TDS ratio past 44% first.

Sources

• Mortgage loan insurance — CMHC
• Minimum down payment — CMHC
• Guideline B-20: Residential Mortgage Underwriting Practices and Procedures — OSFI
• Mortgage stress test — Financial Consumer Agency of Canada

This article is for general educational purposes only and does not constitute financial or mortgage advice. Down payment tiers, insurance requirements, stress-test rules, and amortization limits can change — confirm current rules with a licensed mortgage professional or financial institution before making a purchase decision.

What to do next

If you're still deciding whether buying makes sense right now compared to renting, that's worth working through before the mortgage mechanics matter at all. For the savings side of a home purchase, FHSA Explained covers the account specifically built for a first home down payment, and can be combined with the RRSP Home Buyers' Plan. If a rate change or economic update is part of what's prompting the question, see Bank of Canada Rate Hold — What It Means for You for how central bank decisions flow through to mortgage pricing. For choosing between a fixed and variable rate specifically, see Fixed vs. Variable Mortgage in 2026, and for the current state of the housing market itself, see Canada's Housing Market Slowdown: What September's Numbers Mean for Buyers and Sellers.