Mortgage Approval 101: GDS & TDS Explained

Hummingbird Mortgages • September 3, 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.


Nate Atkin
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What Older Canadians Should Know About Mortgage Financing

By Hummingbird Mortgages • July 8, 2026
Retirement doesn’t always mean a mortgage-free life anymore. And that’s okay. Between higher home prices, rising living costs, and longer life expectancy, many Canadians are choosing to retire with a mortgage or refinance later in life to create more flexibility. The goal isn’t perfection. It’s having options that actually support the life you want to live. If you’re thinking about how a mortgage fits into your retirement years, you’re not alone—and you’re not out of options. Why work with an independent mortgage professional? Because retirement financing is not one-size-fits-all. Unlike a single bank, an independent mortgage professional can look across multiple lenders and solutions to find what truly fits your income, equity, and long-term plans—not just what one institution offers. Mortgage options available in retirement Traditional Mortgage Solutions Many retirees still qualify for standard mortgages. Pension income, investment income, and other retirement sources can often be used to support an application. If you have good equity and solid credit, this is often the lowest-cost option. Reverse Mortgages For homeowners 55+, a reverse mortgage can unlock tax-free equity from your home with no monthly payments required. There’s no income verification or medical questions, making it a helpful option for those who want to improve cash flow while staying in their home. Home Equity Line of Credit (HELOC) A HELOC allows you to access your home equity as needed and only pay interest on what you use. Many retirees appreciate the flexibility and like consolidating income and expenses in one place. Private Financing Sometimes life throws a curveball. If timing, income, or credit create challenges, private financing can act as a short-term bridge. It’s not usually the first choice, but it can provide solutions when traditional lenders can’t. If you’re approaching retirement—or already there—and wondering how your mortgage fits into the picture, let’s talk. A clear plan can make retirement feel a lot more secure and a lot less stressful.

What Online Mortgage Calculators Can—and Can’t—Tell You

By Hummingbird Mortgages • July 1, 2026
What Online Mortgage Calculators Can—and Can’t—Tell You Online mortgage calculators are everywhere—and on the surface, they seem like a no-brainer. You plug in some numbers, and out pops what you can “afford.” Simple, right? Not quite. While the math itself is correct, the story behind those numbers is often misleading. Mortgage qualification isn’t just about numbers—it’s about context, risk, and lender policy. And that’s where calculators fall short. The Numbers Are Accurate—but the Picture Isn’t An online calculator can show you what a payment might look like at a given interest rate, or how making extra payments could reduce your amortization. That’s useful information! But when it comes to mortgage qualification , calculators don’t account for the many variables that lenders consider, such as: Your credit history and score Employment type (salary, self-employed, contract) Outstanding debts and monthly obligations Assets, savings, and down payment source The property type and location you’re buying Lenders evaluate all these factors through their internal risk models. That means two people entering the exact same numbers into a calculator could receive very different results when they actually apply for a mortgage. Why Online Calculators Can Mislead You When you see a “How much can I afford?” or “Mortgage Qualification” calculator online, it’s easy to treat the result as fact. But these tools don’t know your financial story—they only crunch the data you enter. A calculator can’t predict how a lender views your risk, how new mortgage rules apply to your file, or how things like spousal support, car loans, or variable income will impact approval. In short: calculators estimate payments, not qualification . Use Calculators the Right Way Don’t get us wrong—online calculators still have value. Use them to explore different “what-if” scenarios: How do payments change with different down payment amounts? How would a rate increase affect affordability? What if you added $100 a month to your payments? These tools are great for helping you understand your comfort zone. Just remember: they’re a starting point, not a green light. The Real First Step: Get a Pre-Approval If you’re serious about buying a home, skip the guesswork and get a mortgage pre-approval . It’s quick, free, and gives you real-world clarity on what you can afford. A pre-approval looks at your full financial picture—income, credit, debts, assets—and provides a framework for your purchase price, payment range, and rate options. It’s the only way to get a reliable answer to the question, “What can I really afford?” Final Thoughts Online calculators are convenient, but they can’t replace expert advice. Think of them as a starting point, not a solution. A professional mortgage broker can interpret the numbers, navigate lender policies, and tailor your financing strategy to your actual situation. If you’d like help understanding your true buying power—or want to get pre-approved with confidence— reach out anytime . I’d be happy to walk you through your options and help you make sense of the numbers.