What Are GDS/TDS Ratios Anyways?

Carmelo Mamertino • March 26, 2025

One of the major qualifiers lenders look at when considering your application for mortgage financing is your debt service ratios.


Now, before we get started, if you prefer to have someone walk through these calculations with you, assess your financial situation, and let you know exactly where you stand, let’s connect. There is no use in dusting off the calculator and running the numbers yourself when we can do it for you!


However, if you’re someone who likes to know the nitty-gritty of how things work instead of simply accepting that's just the way it is, this article is for you. But be warned, there are a lot of mortgage words and some math ahead; with that out of the way, let’s get started!

 

“Debt servicing” is the measure of your ability to meet all of your financial obligations. There are two ratios that lenders examine to determine whether you can debt service a mortgage.


The first is called the “gross debt service” ratio, or GDS, which is the percentage of your monthly household income that covers your housing costs. The second is called the “total debt service” ratio, or TDS, which is the percentage of your monthly household income covering your housing costs and all your other debts.


GDS is your income compared to the cost of financing the mortgage, including your proposed mortgage payments (principal and interest), property taxes, and heat (PITH), plus a percentage of your condo fees (if applicable).


Here’s how to calculate your GDS.


Principal + Interest + Taxes + Heat / Gross Annual Income


Your TDS is your income compared to your GDS plus the payments made to service any existing debts. Debts include car loans, line of credit, credit card payments, support payments, student loans, and anywhere else you’re contractually obligated to make payments.


Here’s how to calculate your TDS.


Principal + Interest + Taxes + Heat + Other Debts / Gross Annual Income


With the calculations for those ratios in place, the next step is to understand that each lender has guidelines that outline a maximum GDS/TDS. Exceeding these guidelines will result in your mortgage application being declined, so the lower your GDS/TDS, the better.


If you don’t have any outstanding debts, your GDS and TDS will be the same number. This is a good thing!


The maximum ratios vary for conventional mortgage financing based on the lender and mortgage product being offered. However, if your mortgage is high ratio and mortgage default insurance is required, the maximum GDS is 39% with a maximum TDS of 44%.


So how does this play out in real life? Well, let’s say you’re currently looking to purchase a property with a payment of $1700/mth (PITH), and your total annual household income is $90,000 ($7500/mth). The calculations would be $1700 divided by $7500, which equals 0.227, giving you a gross debt service ratio of 22.7%.


A point of clarity here. When calculating the principal and interest portion of the payment, the Government of Canada has instituted a stress test. It requires you to qualify using the government's qualifying rate (which is higher), not the actual contract rate. This is true for both fixed and variable rate mortgages.


Now let’s continue with the scenario. Let’s say that in addition to the payments required to service the property, you have a car payment of $300/mth, child support payments of $500/mth, and between your credit cards and line of credit, you’re responsible for another $700/mth. In total, you pay $1500/mth. So when you add in the $1700/mth PITH, you arrive at a total of $3200/mth for all of your financial obligations. $3200 divided by $7500 equals 0.427, giving you a total debt service ratio of 42.7%.


Here’s where it gets interesting. Based on your GDS alone, you can easily afford the property. But when you factor in all your other expenses, the TDS exceeds the allowable limit of 42% (for an insured mortgage anyway). So why does this matter? Well, as it stands, you wouldn’t qualify for the mortgage, even though you are likely paying more than $1700/mth in rent.


So then, to qualify, it might be as simple as shuffling some of your debt to lower payments. Or maybe you have 10% of the purchase price saved for a downpayment, changing the mortgage structure to 5% down and using the additional 5% to pay out a portion of your debt might be the difference you need to bring it all together.


Here’s the thing, as your actual financial situation is most likely different than the one above, working with an independent mortgage professional is the best way to give yourself options. Don’t do this alone. Your best plan is to seek and rely on the advice provided by an experienced independent mortgage professional. While you might secure a handful of mortgages over your lifetime, we do this every day with people just like you.


It’s never too early to start the conversation about mortgage qualification. Going over your application and assessing your debt service ratios in detail beforehand gives you the time needed to make the financial moves necessary to put yourself in the best financial position.


So if you find yourself questioning what you can afford or if you want to discuss your GDS/TDS ratios to understand the mortgage process a little better, please get in touch. It would be a pleasure to work with you, we can get a preapproval started right away.


Carmelo Mamertino

Why a Mortgage Pre-Approval Protects Both Your Head and Your Heart

By Carmelo Mamertino • May 20, 2026
Why a Mortgage Pre-Approval Protects Both Your Head and Your Heart There’s no denying it—buying a home is an emotional journey. In a competitive market, it can feel like you need to stretch beyond your comfort zone or bid above asking just to have a chance. That pressure can make it hard to separate what you want from what you can realistically afford. One of the biggest pitfalls buyers face is falling in love with a home that’s outside their price range. Once that happens, every other property seems like a compromise—even the ones that might have been a perfect fit otherwise. The best way to avoid this heartache? Get pre-approved before you start shopping. What a Pre-Approval Does for You A mortgage pre-approval gives you more than just a number—it provides clarity, confidence, and protection: Know your buying power : Shop within your true price range and avoid disappointment. Spot potential roadblocks : Uncover issues like credit bureau errors before you make an offer. Get organized : Learn exactly what documentation you’ll need so there are no surprises. Lock in a rate : Many lenders hold your rate for 30–120 days, giving you peace of mind if rates rise. Save yourself heartache : Protect yourself from falling for a home you can’t afford. Head vs. Heart Buying a home is about balance. Your head tells you what’s financially sound, your heart tells you what feels right—and both matter. A pre-approval helps bring those two sides together, so you can make confident choices without emotional stress clouding your judgment. The Bottom Line Looking at properties for fun is one thing—but if you’re serious about buying, a pre-approval is the smartest first step you can take. It sets realistic expectations, saves time, and protects your emotions along the way. If you’d like to explore your options and get pre-approved, I’d be happy to walk through the process with you. Let’s make sure you’re ready to shop with confidence.

Get Unbiased Advice: Work with an Independent Mortgage Pro

By Carmelo Mamertino • May 13, 2026
Why Work With an Independent Mortgage Professional? If you’re in the market for a mortgage, here’s the most important thing to know: Working with an independent mortgage professional can save you money and provide better options than dealing directly with a single bank. If that’s all you read—great! But if you’d like to understand why that statement is true, keep reading. The Best Mortgage Isn’t Just About the Lowest Rate It’s easy to fall for slick marketing that promotes ultra-low mortgage rates. But the lowest rate doesn’t always mean the lowest cost . The best mortgage is the one that costs you the least amount of money over time —not just the one with the flashiest headline rate. Things like: Prepayment penalties Portability Flexibility to refinance Amortization structure Fixed vs. variable terms …can all affect the true cost of your mortgage. An independent mortgage professional looks beyond the rate. They’ll help you find a product that fits your unique financial situation , long-term goals, and lifestyle—so you’re not hit with expensive surprises down the road. Save Time (and Your Sanity) Applying for a mortgage can be complicated. Every lender has different rules, documents, and policies—and trying to navigate them all on your own can be time-consuming and frustrating. When you work with an independent mortgage professional: You fill out one application They shop that application across multiple lenders You get expert advice tailored to your needs This means less paperwork , less stress , and more confidence in your options. Get Unbiased Advice That Puts You First Bank specialists work for the bank. Their job is to sell you that bank’s mortgage products—whether or not it’s the best deal for you. Independent mortgage professionals work for you. They’re provincially licensed, and their job is to help you: Compare multiple lenders Understand the fine print Make informed, long-term financial decisions And the best part? Their services are typically free to you . Mortgage professionals are paid a standardized fee by the lender when a mortgage is placed—so you get expert guidance without any out-of-pocket cost. Access More Mortgage Options When you go to your bank, you’re limited to that bank’s mortgage products. When you go to an independent mortgage professional, you get access to: Major banks Credit unions Monoline lenders (who only offer mortgages) Alternative and private lenders (if needed) That’s far more choice , and a much better chance of finding a mortgage that truly fits your needs and goals. The Bottom Line If you want to: Save money over the life of your mortgage Save time by avoiding unnecessary back-and-forth Access more lenders and products Get honest, client-first advice …then working with an independent mortgage professional is one of the smartest decisions you can make. Let’s Make a Plan That Works for You If you're ready to talk about mortgage financing—or just want to explore your options—I'm here to help. Let's connect and put together a strategy that makes sense for your goals and your future. Reach out anytime. I’d be happy to help.