What Are GDS and TDS Ratios?
Understanding the Mortgage Calculations That Can Make or Break Your Approval
Quick Answer
GDS (Gross Debt Service) and TDS (Total Debt Service) ratios are affordability calculations used by Canadian mortgage lenders to determine whether you can comfortably afford a mortgage. GDS measures the percentage of your gross income required to cover housing expenses, while TDS includes housing costs plus all other monthly debt obligations. Even borrowers with excellent credit can be declined if these ratios exceed lender guidelines. Understanding GDS and TDS before applying for a mortgage can improve your chances of approval and help you choose the right mortgage strategy.
Table of Contents
- What Are GDS and TDS Ratios?
- Why Do Mortgage Lenders Use Them?
- What Is GDS?
- What Is TDS?
- How Is GDS Calculated?
- How Is TDS Calculated?
- What Expenses Count?
- What Ratios Do Canadian Lenders Typically Accept?
- Why Good Credit Alone Is Not Enough
- How Mortgage Brokers Help Improve Debt Ratios
- Special Considerations for Self-Employed Borrowers
- Frequently Asked Questions
- Related Mortgage Learning Centre Articles
What Are GDS and TDS Ratios?
“I have excellent credit. Why was my mortgage declined?”
It is one of the most common questions borrowers ask.
Many assume that a strong credit score guarantees mortgage approval. In reality, credit is only one piece of the underwriting process. A lender must also determine whether your income can comfortably support your mortgage payments and other financial obligations.
That is where Gross Debt Service (GDS) and Total Debt Service (TDS) ratios come into play.
These calculations are among the most important numbers a lender reviews. Understanding them before you apply can save time, reduce frustration, and improve your chances of approval.
Why Do Mortgage Lenders Use Them?
Mortgage lenders have two responsibilities.
First, they want to protect their investment.
Second, they want to ensure borrowers are not taking on more debt than they can reasonably afford.
GDS and TDS ratios provide a standardized way to measure affordability.
Rather than looking only at your salary, lenders compare your monthly debt obligations to your gross monthly income.
This helps answer a simple question:
Can this borrower realistically afford this mortgage over the long term?
What Is Gross Debt Service (GDS)?
Gross Debt Service measures the percentage of your gross monthly income required to cover your housing costs.
Housing costs generally include:
- Mortgage principal and interest
- Property taxes
- Heating costs
- Fifty percent of condominium fees (when applicable)
The lower your GDS ratio, the more comfortably you can afford your home.
Example
Imagine your household earns:
$120,000 per year
Gross monthly income:
$10,000
Monthly housing costs:
- Mortgage Payment: $2,600
- Property Taxes: $400
- Heating: $150
- Condo Fees (50%): $150
Total Housing Costs:
$3,300
GDS Calculation:
$3,300 ÷ $10,000 = 33%
In this example, your GDS ratio is approximately 33%, which generally falls within many lenders’ acceptable guidelines.
What Is Total Debt Service (TDS)?
TDS expands on GDS by including all recurring monthly debt obligations.
These may include:
- Vehicle loans
- Personal loans
- Student loans
- Credit card minimum payments
- Lines of credit
- Child support
- Spousal support
Since TDS reflects your complete financial picture, it is often the deciding factor in mortgage approval.
Example
Continuing the previous example:
Housing Costs:
$3,300
Additional Monthly Debts:
- Car Loan: $550
- Credit Card Minimum Payment: $150
- Line of Credit: $200
Total Monthly Debt:
$4,200
TDS Calculation:
$4,200 ÷ $10,000 = 42%
This borrower now has a 42% TDS ratio.
What Expenses Count?
Every lender has underwriting guidelines, but most include:
Included in GDS
- Mortgage payment
- Property taxes
- Heating costs
- 50% of condo fees
Included in TDS
Everything above plus:
- Car payments
- Credit card payments
- Lines of credit
- Student loans
- Personal loans
- Support payments
Some situations require additional calculations, particularly for rental properties, self-employed borrowers, or commercial lending.
What Ratios Do Canadian Lenders Typically Accept?
While guidelines vary by lender and mortgage insurer, many traditional lenders commonly look for:
| Ratio | Typical Guideline |
|---|---|
| GDS | Approximately 39% or less |
| TDS | Approximately 44% or less |
These are guidelines—not guarantees.
Some lenders may allow higher ratios depending on:
- Credit history
- Down payment
- Net worth
- Liquid assets
- Strength of the application
- Type of property
- Compensating factors
Alternative and private lenders may also consider higher debt ratios under certain circumstances.
Why Good Credit Is Not Enough
This is where many borrowers become confused.
They assume:
“My credit score is over 800.”
Yet they are still declined.
Why?
Because lenders evaluate three primary areas:
- Credit
- Income
- Affordability
Excellent credit cannot compensate for insufficient income or excessive monthly debt obligations.
Likewise, a high income may still result in a decline if monthly debts are too high.
Mortgage approval is about the entire financial picture—not just one number.
Can You Improve Your GDS or TDS Ratios?
Often, yes.
Possible strategies include:
- Paying off smaller debts
- Increasing the down payment
- Extending the amortization (where permitted)
- Choosing a lower-priced property
- Consolidating high-interest debt
- Adding a co-borrower
- Selecting a lender whose underwriting guidelines better fit your situation
This is one of the greatest advantages of working with an experienced mortgage broker.
Expert Insight from Mike Cara
“Many borrowers focus on their credit score because it is easy to understand. However, lenders look much deeper than that. GDS and TDS ratios tell the story of affordability. In many cases, the right mortgage strategy—not simply a lower interest rate—can improve those ratios and lead to an approval that may not have been possible otherwise.”
Special Considerations for Self-Employed Borrowers
Debt ratios become even more important for self-employed individuals.
Business write-offs can reduce taxable income, making affordability appear weaker than it actually is.
Fortunately, some lenders offer programs specifically designed for self-employed borrowers, using alternative methods of income verification.
Choosing the right lender can make a significant difference.
Frequently Asked Questions
Is GDS more important than TDS?
Both are important. However, TDS often carries greater weight because it measures your total financial obligations.
Can excellent credit offset high debt ratios?
Sometimes, but not always. Strong credit may strengthen your application, but lenders still need to be confident you can comfortably afford the mortgage.
Are GDS and TDS the same for every lender?
No. Each lender has its own underwriting policies, although many follow similar industry guidelines.
Do private lenders use GDS and TDS?
Many private lenders review debt ratios, but they may place greater emphasis on property equity, exit strategy, and overall risk.
Can a mortgage broker help improve my debt ratios?
Yes. A mortgage broker can identify lenders whose guidelines best match your financial profile and recommend strategies to strengthen your application before it is submitted.
Related Mortgage Learning Centre Articles
To better understand mortgage affordability, continue with these resources:
- How to Choose the Right Mortgage Broker
- Fixed vs Variable Mortgages
- Mortgage Renewal Guide
- Mortgage Refinancing Explained
- Debt Consolidation Mortgages
- Self-Employed Mortgages
- Private Mortgages
- Commercial Mortgages
- First-Time Homebuyer Guide
- Mortgage Pre-Approval Guide
These articles are designed to help homeowners and buyers make informed borrowing decisions and to support a comprehensive mortgage knowledge library.
Your Next Step
If you are unsure whether your income, debts, or affordability ratios meet today’s lending guidelines, seeking professional advice before submitting an application can save time and prevent disappointment.
At MikeCara.ca, Mike Cara helps homebuyers, homeowners, investors, and self-employed borrowers understand their borrowing capacity and develop mortgage strategies that fit their financial goals.
Before you apply, learn where you stand. A well-planned mortgage application begins with understanding your numbers.
