Mortgage Approval 101: GDS & TDS Explained

Erik Sepper • August 20, 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.


ERIK SEPPER 
MORTGAGE AGENT

CONTACT ME

How Your Loans and Spending Habits Are Quietly Shaping Your Credit Score

By Erik Sepper • April 10, 2026
Your credit score is one of the most important numbers in your financial life — especially when it comes to getting a mortgage. But for most Canadians, how that number actually gets calculated remains a bit of a mystery.

Going Through a Divorce? Don’t Let Your Credit Take the Hit

By Erik Sepper • April 8, 2026
Going Through a Divorce? Don’t Let Your Credit Take the Hit Divorce is stressful enough without adding financial fallout to the mix. Between lawyers, paperwork, and emotional strain, it’s easy to overlook how a separation can impact your credit. But your financial future depends on protecting it now—because long after the dust settles, a damaged credit score can linger. Here are a few smart steps to help keep your credit strong and your finances steady as you move forward. 1. Take Control of Joint Debts When it comes to joint debt, both parties are equally responsible—no matter what your divorce agreement says. If your ex misses a payment on an account with your name attached, your credit takes the hit too. Go through all joint credit cards, loans, and lines of credit. Wherever possible: Close joint accounts to stop future shared use. Transfer balances to the person responsible for repayment. Notify lenders in writing of any changes to account ownership. Once everything is updated, pull your credit report after three to six months to confirm all joint accounts have been closed and reporting correctly. Mistakes happen—stay proactive to prevent surprises later. 2. Open Your Own Bank Accounts Separation means financial independence, and that starts with your own banking. Open a new chequing account in your name only and redirect your pay deposits and bill payments there. At the same time, close any joint bank accounts and change passwords on existing online banking and credit profiles. Even in peaceful separations, shared access can cause confusion—or conflict. Protect yourself by ensuring your money and information are secure. 3. Start Building Credit in Your Name If most of your past credit was tied to your spouse’s name, now’s the time to establish your own. Apply for a small personal credit card or secured credit product . Use it sparingly and pay it off in full each month. This helps you build a solid individual credit history, setting the stage for future goals like buying a home, refinancing, or starting fresh financially. 4. Keep an Eye on Your Credit Monitor your credit report regularly for errors or unexpected changes. You can request free reports from both major credit bureaus in Canada— Equifax and TransUnion —once a year. Tracking your credit isn’t just about catching mistakes; it helps you see your progress as you rebuild your financial independence. Final Thoughts Divorce can be emotionally draining, but protecting your credit doesn’t have to be complicated. By taking a few careful steps now—closing joint accounts, building credit in your name, and monitoring your reports—you’ll safeguard your financial health and gain peace of mind as you start your next chapter. If you’d like personalized guidance on managing credit during or after a divorce, reach out anytime. I’d be happy to walk you through your options.

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

By Erik Sepper • April 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.