Mortgage Approval 101: GDS & TDS Explained

Diane Buchanan • October 22, 2025

Can You Afford That Mortgage? Let’s Talk About Debt Service Ratios

One of the biggest factors lenders look at when deciding whether you qualify for a mortgage is something called your debt service ratios. It’s a financial check-up to make sure you can handle the payments—not just for your new home, but for everything else you owe as well.


If you’d rather skip the math and have someone walk through this with you, that’s what I’m here for. But if you like to understand how things work behind the scenes, keep reading. We’re going to break down what these ratios are, how to calculate them, and why they matter when it comes to getting approved.


What Are Debt Service Ratios?

Debt service ratios measure your ability to manage your financial obligations based on your income. There are two key ratios lenders care about:

  1. Gross Debt Service (GDS)
    This looks at the percentage of your income that would go toward housing expenses only.

   2. Total Debt Service (TDS)
       This includes your housing costs plus all other debt payments—car loans, credit cards, student loans, support payments, etc.


How to Calculate GDS and TDS

Let’s break down the formulas.


GDS Formula:

(P + I + T + H + Condo Fees*) ÷ Gross Monthly Income


Where:

P = Principal

I = Interest

T = Property Taxes

H = Heat


Condo fees are usually calculated at 50% of the total amount


TDS Formula:

(GDS + Monthly Debt Payments) ÷ Gross Monthly Income


These ratios tell lenders if your budget is already stretched too thin—or if you’ve got room to safely take on a mortgage.


How High Is Too High?


Most lenders follow maximum thresholds, especially for insured (high-ratio) mortgages.

As of now, those limits are typically:

GDS: Max 39%

TDS: Max 44%


Go above those numbers and your application could be declined, regardless of how confident you feel about your ability to manage the payments.


Real-World Example

Let’s say you’re earning $90,000 a year, or $7,500 a month.

You find a home you love, and the monthly housing costs (mortgage payment, property tax, heat) total $1,700/month.


GDS = $1,700 ÷ $7,500 = 22.7%


You’re well under the 39% cap—so far, so good.


Now factor in your other monthly obligations:

  • Car loan: $300
  • Child support: $500
  • Credit card/line of credit payments: $700
    Total other debt = $1,500/month


Now add that to the $1,700 in housing costs:
TDS = $3,200 ÷ $7,500 = 42.7%


Uh oh. Even though your GDS looks great, your TDS is just over the 42% limit. That could put your mortgage approval at risk—even if you’re paying similar or higher rent now.


What Can You Do?

In cases like this, small adjustments can make a big difference:

  • Consolidate or restructure your debts to lower monthly payments
  • Reallocate part of your down payment to reduce high-interest debt
  • Add a co-applicant to increase qualifying income
  • Wait and build savings or credit strength before applying


This is where working with an experienced mortgage professional pays off. We can look at your entire financial picture and help you make strategic moves to qualify confidently.


Don’t Leave It to Chance

Everyone’s situation is different, and debt service ratios aren’t something you want to guess at. The earlier you start the conversation, the more time you’ll have to improve your numbers and boost your chances of approval.


If you're wondering how much home you can afford—or want help analyzing your own GDS and TDS—let’s connect. I’d be happy to walk through your numbers and help you build a solid mortgage strategy.


DIANE BUCHANAN
 Mortgage Broker

LET'S TALK

Bank of Canada Holds Rate at 2.25% — July 15, 2026

By Diane Buchanan • July 15, 2026
The Bank of Canada announced today that it is holding its target for the overnight rate at 2.25%, with the Bank Rate at 2.5% and the deposit rate at 2.20%. The tone of today's announcement is notably more optimistic than previous months. Here's what's changed and what it means for you.

Stress-Testing Your Mortgage Affordability: Why It Matters

By Diane Buchanan • July 8, 2026
Buying a home is one of the biggest financial commitments you’ll ever make. That’s why lenders want to be sure you can handle your mortgage payments—not just today, but also if interest rates rise in the future. This is where the mortgage stress test comes in. Many Canadians hear the term but aren’t entirely sure what it means or how it affects them. Let’s break it down in plain language. What Is the Mortgage Stress Test? The stress test is a rule introduced by the federal government that requires all mortgage applicants to qualify at a higher rate than the one they’ll actually pay. Currently, you must qualify at the greater of your contract rate + 2% or the benchmark qualifying rate (set by the Office of the Superintendent of Financial Institutions). For example: If your lender offers you a 5-year fixed mortgage at 5.25%, you must show you could still afford the payments at 7.25% . Even if rates don’t rise that high, the stress test ensures you won’t be overextended if they do. Why Does It Matter? The stress test protects both borrowers and lenders by: Preventing over-borrowing : It ensures you don’t take on more debt than you can realistically handle. Preparing for rate hikes : With interest rates fluctuating, it’s a safeguard against sudden increases. Strengthening financial stability : It lowers the risk of defaults, protecting the housing market as a whole. While it can sometimes feel like a barrier—reducing the amount you qualify for—it’s ultimately designed to keep you from becoming “house poor.” How Does It Impact Buyers? The stress test can significantly affect your homebuying budget. For example, without it, you might qualify for a $600,000 mortgage, but with the stress test applied, you may only qualify for $500,000. That doesn’t mean your dream of homeownership is out of reach—it just means you may need to adjust expectations or explore other strategies, such as: Increasing your down payment Paying down existing debts Considering alternative lenders who may have different qualification standards Why Work With a Mortgage Professional? Every lender applies the stress test, but not every lender views your application the same way. An independent mortgage professional can: Shop multiple lenders to find the best fit Run affordability scenarios at different rates Help you understand how much house you can truly afford—without stretching your finances too thin The Bottom Line The mortgage stress test isn’t meant to stop you from buying a home—it’s there to protect you from financial strain down the road. By understanding how it works and planning ahead, you can make smarter choices and buy with confidence. If you’re thinking about purchasing a home, refinancing, or simply want to know how the stress test affects your options, connect with us today. We’ll help you stress-test your budget and find the mortgage solution that works best for you.