GDS/TDS Ratios Explained

Tim Lyon • November 16, 2023

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.

Tim Lyon

Mortgage Consultant

By Tim Lyon October 28, 2025
If you're buying a home with less than 20% down, you'll need something called an insured mortgage. Many borrowers find this confusing at first, especially since it doesn’t refer to insurance for you, the borrower. That’s why I have put together this straightforward breakdown so you understand what insured mortgages are, why they exist, and how they affect your purchase. What Is an Insured Mortgage? A mortgage must be insured when a borrower makes a down payment of less than 20% on a home purchase. The insurance protects the lender (not the borrower) in case the borrower defaults. The insurance is guaranteed by the federal government. So, why do we have this program? It allows borrowers to buy homes with smaller down payments and higher loan-to-value (LTV) ratios. Higher loan-to-value mortgages are inherently more risky because there is not much cushion if the housing market starts to decline. For example, if someone buys a $500,000 home with only 5% down ($25,000), they’ll need a $475,000 mortgage—this is a 95% LTV . If the market drops and the home’s value falls to $470,000, the mortgage would still be $475,000. If the borrower stopped making payments, the lender could lose money after selling the home and paying costs. That kind of loss, multiplied across thousands of borrowers, could threaten the stability of the entire banking system (as we saw in the U.S. in 2008). The mortgage insurance system is designed to prevent that scenario by spreading risk and keeping lenders protected. How Does the Insurance Work? You, the borrower, pay the insurance premium. It's typically added directly to your mortgage balance rather than paid upfront. The cost depends on your down payment size and amortization. Example: Purchase price: $500,000 Down payment: $25,000 (5%) Mortgage amount: $475,000 Insurance premium: 4.2% = $19,950 Total new mortgage: $494,950 The insurance does add cost, but insured mortgages usually offer slightly lower interest rates because the lender's risk is minimal. The rate savings don't fully offset the premium, but they help. The Insurer’s Role For insured mortgages, the insurer’s approval is the most important part of the process. If the insurer won’t approve the file, no lender can. Once the insurer signs off, we can typically find a lender to fund the loan. Canada has three mortgage insurers: CMHC (public) Sagen (private) Canada Guaranty (private) All of the insurers are backed by government guarantees and have to follow similar rules, but each has a few unique programs. Lenders usually choose the insurer, though I sometimes work with them to send a file to a specific insurer if it benefits the borrower. Qualification Rules Because insured mortgages are government-backed, the rules are strict: Debt ratios: 39% of your income can go toward your stress-tested mortgage payment, property taxes, heat, and half of condo fees 44% of your income can go toward the above plus your other debts Down payment: 5% on the first $500,000, 10% on the remainder Maximum purchase price: $1.5 million Amortization: Maximum of 25 years for most buyers; up to 30 years for first-time buyers who qualify under the new federal program Unlike with an uninsured mortgage, where lenders may have some flexibility if your income ratios are slightly above the limits, there is no discretion on an insured mortgage. If your ratios exceed the limits even a little bit, the insurer will decline the application. The Approval Process The process is similar to an uninsured mortgage, with one extra step: We submit your mortgage application to the lender of choice They do their initial review If that looks good, they package it up and send it to the insurer Once the insurer has reviewed and approved it, the file comes back to the lender for final review and approval Common Misunderstandings About Insured Mortgages Many borrowers are surprised to learn the following facts about insured mortgages: You do not need to be a first-time homebuyer to buy with less than 20% down You cannot buy an investment property with less than 20% down You can buy a second home with less than 20% down You cannot refinance an insured mortgage and keep the insurance. If you have an insured mortgage and do refinance, you will lose the insurance. This mostly affects the lender, but it also moves you to uninsured rates. Why Choose an Insured Mortgage? Given the cost and restrictions, why would anyone choose an insured mortgage? The main reason is accessibility . It allows you to buy a home without saving a full 20% down payment, which is increasingly difficult with high home prices and living costs. It can also be a strategic choice. Some buyers prefer to keep more of their savings invested or diversified instead of tying everything up in a down payment. If your investments are earning more than your mortgage costs, keeping that money invested might make financial sense. Real-World Example Let's say you're buying a $600,000 home. Here's how the costs compare between the minimum down payment for an insured mortgage and the minimum down payment for an uninsured mortgage:
By Tim Lyon October 20, 2025
The part of mortgage approval nobody likes but everyone needs