Mortgage Approval 101: GDS & TDS Explained

Niki Cuthbert • January 7, 2026

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.


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Bank of Canada Holds Rate at 2.25% — June 10, 2026

By Niki Cuthbert • June 10, 2026
The Bank of Canada announced today that it is maintaining its target for the overnight rate at 2.25%, with the Bank Rate at 2.5% and the deposit rate at 2.20%. For Canadian homeowners, buyers, and anyone with a mortgage on the horizon — here's what you need to know.

Co-Signing a Mortgage in Canada: Pros, Cons & What to Expect

By Niki Cuthbert • June 3, 2026
Co-Signing a Mortgage in Canada: Pros, Cons & What to Expect Thinking about co-signing a mortgage? On the surface, it might seem like a simple way to help someone you care about achieve homeownership. But before you sign on the dotted line, it’s important to understand exactly what co-signing means—for them and for you. You’re Fully Responsible When you co-sign, your name is on the mortgage—and that makes you just as responsible as the primary borrower. If payments are missed, the lender won’t only go after them; they’ll come after you too. Missed payments or default can damage your credit score and put your financial health at risk. That’s why trust is key. If you’re going to co-sign, make sure you have a clear picture of the borrower’s ability to manage payments—and consider monitoring the account to protect yourself. You’re Committed Until They Can Stand Alone Co-signing isn’t temporary by default. Even once the initial mortgage term ends, you won’t automatically be removed. The borrower has to re-qualify on their own, and only then can your name be taken off. If they don’t qualify, you stay on the mortgage for another term. Before agreeing, talk openly about expectations: How long might you be on the mortgage? What’s the plan for eventually removing you? Having these conversations upfront prevents surprises later. It Affects Your Own Borrowing Power When lenders calculate your debt service ratios, the co-signed mortgage counts as your debt—even if you never make a payment on it. This could reduce how much you’re able to borrow in the future, whether it’s for your own home, an investment property, or even refinancing. If you see another mortgage in your future, you’ll want to consider how co-signing could limit your options. The Upside: Helping Someone Get Ahead On the positive side, co-signing can be life-changing for the borrower. You could be helping a family member or friend buy their first home, start building equity, or take an important step forward financially. If handled with clear expectations and trust, it can be a meaningful way to support someone you care about. The Bottom Line Co-signing a mortgage comes with both risks and rewards. It’s not a decision to take lightly, but with careful planning, transparency, and professional advice, it can be done responsibly. If you’re considering co-signing—or want to explore safer alternatives—let’s connect. I’d be happy to walk you through what to expect and help you decide if it’s the right move for you.