GDS and TDS Ratios in Canada: Rebuild the Mortgage Qualification Math

Gross debt service and total debt service ratios are two lender tests that compare selected monthly obligations with gross income. GDS measures housing costs. TDS adds other debt obligations.

The ratios look simple, but a small input difference can move a borrower from approval to decline. The mortgage payment may be calculated at a stress-test rate rather than the offered rate, only part of a condo fee may enter the worksheet, a revolving balance may receive a minimum assumed payment, and income may be reduced or excluded.

This guide shows how to reproduce the worksheet, identify the disputed input, and build a second budget that answers the more useful household question: can you carry the home after tax and still fund repairs, savings, and ordinary life?

!GDS and TDS mortgage worksheet showing verified income, qualifying payment, housing costs, debt payments, ratios, and household cash-flow check

Short answer: calculate three numbers, not one

Prepare three views before setting a price ceiling:

1. Lender GDS: qualifying housing costs divided by accepted gross monthly income.
2. Lender TDS: qualifying housing costs plus accepted monthly debt obligations, divided by accepted gross monthly income.
3. Household carrying ratio: the real payment and all ownership costs divided by reliable after-tax cash income.

CMHC's current GDS and TDS calculation guidance states 39% and 44% limits for its insured underwriting and explains how it treats common inputs. Those ceilings do not promise approval, bind every lender in every transaction, or describe a comfortable personal budget.

CMHC's homebuying workbook also presents 32% GDS and 40% TDS as general affordability rules before stating the higher insured qualification limits. Treat qualification and resilience as separate decisions.

The formulas

At a monthly level:

GDS = qualifying housing costs ÷ accepted gross monthly income × 100

TDS = (qualifying housing costs + qualifying other debt) ÷ accepted gross monthly income × 100

Housing costs commonly include:

• mortgage principal and interest at the qualifying payment;
• property taxes;
• heating cost;
• 50% of condominium fees where CMHC treatment applies;
• 100% of site or ground rent for relevant chattel or leasehold loans.

TDS then adds the lender's recognized payments for credit cards, lines of credit, vehicle loans or leases, student loans, support, and other obligations. The exact treatment can differ by lender, insurer, product, credit profile, and documentation.

Do not copy a web calculator result into an offer decision without obtaining the lender or broker's input assumptions.

Start with accepted income, not household income

The denominator is not automatically every dollar that enters the household. A lender decides whether income is stable, continuous, documented, and acceptable under its policy.

Create an income reconciliation:

Income source	Current amount	Lender amount	Evidence	Reason for difference
Base salary			Job letter, pay stubs
Bonus/overtime			T4s, notices of assessment	Average or excluded
Commission			Tax and employer records	Multi-year treatment
Self-employment			T1, NOA, financials	Add-backs/policy
Pension/benefit			Statements, tax slips	Continuance
Rental income			Lease, tax, appraisal	Offset or percentage
Support received			Agreement, deposits	Documentation
Accepted annual total

Divide the accepted annual total by 12. If two applicants earn $90,000 and $60,000 in base salary, their initial gross monthly income is $12,500. If the lender excludes a $15,000 hoped-for bonus, leave it out of the qualification worksheet even if the family expects to receive it.

Variable income is where online estimates often overstate capacity. Ask the mortgage professional which years, averages, declines, probation periods, contracts, and business expenses affect the amount.

Calculate the qualifying mortgage payment

Federally regulated lenders require borrowers to qualify at a rate above the contract payment. The Financial Consumer Agency of Canada's current mortgage preparation guidance says banks use the higher of:

• 5.25%; or
• the negotiated mortgage rate plus two percentage points.

The rule applies to insured and uninsured mortgages at banks. Other lenders may also use a stress test or their own underwriting rules.

If the offered rate is 4.60%, the qualifying rate under that test is 6.60%, not 5.25%. If the offered rate is 3.00%, the qualifying rate is 5.25%, because it is higher than 5.00%.

The qualifying payment also depends on loan amount, amortization, payment frequency, compounding convention, and any mortgage-insurance premium added to the loan. Use the lender's calculated payment for the application rather than substituting the actual contract payment.

For scenario planning, the CalculatorVillage mortgage calculator can show payment sensitivity. Reconcile its assumptions with the lender worksheet before relying on it.

Build PITH line by line

Mortgage professionals often refer to principal, interest, taxes, and heat as PITH. For ratio work, record every component separately:

Housing input	Monthly amount	Source
Qualifying principal and interest		Lender worksheet
Property tax		Current bill/municipal estimate
Heat		Actual record or lender estimate
Included condo fee		Fee statement × policy percentage
Site/ground rent		Lease and lender treatment
Qualifying housing total

Annual property tax should be divided by 12 even if the municipality collects on another schedule. For a new build or reassessed property, the current interim bill may understate the completed-home tax. Estimate the finished value and ask the municipality or lawyer about likely timing.

Heat is not the entire utility bill. CMHC says mortgage professionals should ask for monthly heating cost and use actual records when the borrower provides them. A lender may use a standard estimate when the address has no reliable history.

CMHC includes 50% of condo fees in GDS and TDS. The household must still pay 100%, so place the other half in the after-tax budget. Review what the fee excludes with the condo-fee budget guide.

Worked GDS calculation

Assume accepted gross income of $150,000 a year, or $12,500 a month. The lender worksheet contains:

• qualifying mortgage payment: $3,650;
• property tax: $500;
• heat: $120;
• monthly condo fee: $600, with 50% included.

Qualifying housing cost is:

$3,650 + $500 + $120 + $300 = $4,570

GDS is:

$4,570 ÷ $12,500 × 100 = 36.56%

That example is below 39% but above CMHC's 32% general affordability rule. The distinction matters: it may fit an insured underwriting ceiling while leaving less room for tax, the excluded half of the condo fee, maintenance, insurance, and savings.

Add every recognized debt for TDS

Prepare a debt table from current statements and the credit report:

Obligation	Balance	Contract payment	Lender payment	End date
Credit card				Revolving
Unsecured line				Revolving
Secured line				Revolving
Vehicle loan
Vehicle lease
Student loan
Support
Other mortgage

CMHC's professional guidance says unsecured lines of credit and credit cards receive a monthly amount of at least 3% of the outstanding balance for its calculation. A $12,000 balance can therefore add at least $360 a month under that method, even if a statement minimum is lower.

Term debt generally uses the required payment, subject to lender policy. Do not omit a vehicle payment because it ends soon unless the mortgage professional confirms it can be excluded and records the evidence.

Credit limits can matter even when ratios use outstanding balances. A lender may request repayment or closure, and using the account before closing can change qualification. Keep the financing condition active until the lender has reviewed the property, borrower, and current debt position.

Worked TDS calculation

Continue the earlier example with qualifying housing cost of $4,570 and add:

• vehicle loan: $525;
• student loan: $250;
• credit-card assumed payment: $240.

Total qualifying obligations are $5,585. TDS is:

$5,585 ÷ $12,500 × 100 = 44.68%

GDS passed the illustrated CMHC ceiling while TDS did not. The binding constraint is other debt, not the property alone.

Paying off an obligation may help, but confirm the lender's conditions. A payoff might have to occur before approval, from verified funds outside the down payment and closing reserve, with an account statement or closure letter. Moving debt to another account without reducing the recognized payment does not solve the ratio.

Find the binding constraint mathematically

Instead of asking only “How much mortgage can we get?”, calculate available monthly room.

At a 39% GDS ceiling with $12,500 accepted monthly income:

$12,500 × 39% = $4,875 maximum qualifying housing cost

After $500 tax, $120 heat, and $300 included condo fee, $3,955 remains for the qualifying mortgage payment.

At a 44% TDS ceiling:

$12,500 × 44% = $5,500 maximum total obligations

After $1,015 of other debt, only $4,485 remains for housing. TDS is therefore binding and permits $530 less qualifying housing cost than GDS.

This calculation tells the household what could change the result: lower price, larger down payment, documented income, lower tax/fees, or genuinely retired debt. It also exposes an input error quickly.

Run an input-sensitivity table before changing the application

One ratio result does not show which change produces a meaningful improvement. Ask the mortgage professional to recalculate a small set of controlled scenarios while keeping every other input constant.

Scenario	Income	Housing cost	Other debt	GDS	TDS	Cash required
Current file
Purchase price lower by $25,000
Down payment higher by $25,000
Vehicle debt repaid
Revolving balance repaid
Co-borrower added
Lower-tax property

A larger down payment reduces the loan, but the result depends on where the transaction sits in the mortgage-insurance premium schedule and whether the funds remain sufficient for closing. A lower purchase price reduces the loan without consuming more savings and may also reduce transfer tax or property tax, although those effects are location-specific.

Debt repayment can be efficient when a modest cash amount removes a large monthly payment. Suppose $8,000 remains on a vehicle loan with a $525 monthly payment. Retiring it may improve TDS more than adding $8,000 to the down payment, but it also uses liquid cash and may trigger a prepayment charge or leave an inadequate reserve. Compare both lender outputs and the post-closing bank balance.

Adding a co-borrower can raise accepted income but also imports that person's debts, ownership issues, and full contractual exposure. It is not a spreadsheet adjustment to make solely because another scenario misses the limit.

Record the date, rate, lender, product, and policy assumptions beside every scenario. A quote from another lender is comparable only after income, debt, amortization, property, fees, and insurance treatment are aligned.

Check cash to close beside the ratios

A borrower can satisfy GDS and TDS while lacking enough verified cash to complete the purchase. Keep a parallel cash reconciliation:

verified available funds − down payment − deposit already paid − closing costs − required debt payoffs − required reserves = post-closing liquidity

Do not count an expected tax refund, sale proceeds without a firm closing path, an undocumented family transfer, or a line of credit the lender has not accepted. Confirm when each amount must arrive and which statements establish its source.

The remaining balance should cover moving, immediate repairs, utility deposits, and an emergency reserve. If every dollar is assigned to approval conditions, reduce the price before waiving financing.

Qualification ceilings are not guaranteed approvals

CMHC says its 39%/44% treatment considers the application and may apply additional conditions. A lender or another insurer can use lower limits, different income treatment, credit requirements, property restrictions, or other risk controls.

Approval also depends on factors outside these ratios:

• credit history and score;
• down-payment source and verification;
• employment and income stability;
• property appraisal and marketability;
• loan-to-value and insurance eligibility;
• mortgage type and amortization;
• unpaid tax, judgments, support, or contingent liabilities;
• lender portfolio and documentation policy.

A pre-approval usually assesses the borrower with assumed property inputs. It does not approve a specific condominium, rural property, appraisal, title issue, or purchase contract. Re-run the ratios for the actual address.

Rental income requires a disclosed method

For a property with rental income, lenders may use an offset method, a percentage of gross rent, or a net-rental calculation. Owner-occupied units, legal suites, subject-property rent, existing rentals, short-term rent, and market rent can receive different treatment.

Ask for a written reconciliation showing:

• gross rent accepted;
• vacancy or expense reduction;
• whether rent is added to income or offsets property costs;
• mortgage, tax, heat, and fee treatment for each property;
• lease, appraisal, tax return, or bank evidence required;
• treatment of a vacant or unauthorized unit.

Do not add all expected rent to gross income while also omitting the rental property's costs. For an investment decision, use the rental-property cash-flow method after reproducing the lender treatment.

Co-borrowers change both sides of the ratios

Adding a co-borrower can add acceptable income, but it also adds that person's debts and legal responsibility. Use the combined accepted income and combined recognized obligations.

Before adding anyone, model:

• their verified income and employment risk;
• mortgages, guarantees, support, leases, and revolving debt;
• ownership and title plan;
• future borrowing capacity;
• exit, refinance, sale, death, disability, or relationship breakdown;
• tax and estate advice.

A person should not sign a mortgage merely to contribute a denominator. A joint borrower is equally responsible for the unpaid balance under federal consumer guidance, regardless of a private family arrangement.

Convert gross qualification into an after-tax budget

GDS and TDS use gross income, but households pay expenses with cash after income tax and payroll deductions. Build a monthly ownership ledger using conservative net deposits:

Cash use	Monthly amount
Actual mortgage payment
Full property tax
Full condo fee
Heat, electricity, water
Home insurance
Maintenance reserve
Special-assessment reserve
Transportation change
All debt payments
Childcare/support
Food and essentials
Retirement and emergency saving
Discretionary margin

Use the full condo fee, not the 50% underwriting input. Add home insurance even though it is generally outside CMHC's GDS formula. Add a property-specific repair reserve using the home-maintenance budget framework.

Stress the real budget for a renewal rate increase, one income interruption, higher tax and fees, and a repair. If every scenario requires revolving debt, the purchase price is too high for the household even when the lender approves it.

A ratio audit request for your broker or lender

Ask for the worksheet or a written input list containing:

1. accepted annual income by person and source;
2. qualifying rate and amortization;
3. loan amount and insured premium included;
4. qualifying principal-and-interest payment;
5. monthly property tax and heat;
6. condo-fee or ground-rent treatment;
7. every debt and assumed monthly payment;
8. rental-income method;
9. resulting GDS and TDS;
10. product limits, insurer, conditions, and document expiry dates.

If the professional cannot provide exact inputs, you cannot reproduce the result or measure the effect of a different home.

Common calculation errors

Using the offered payment in GDS

The stress-test payment can be materially higher. Obtain the qualifying payment.

Dividing annual costs inconsistently

Convert annual tax and annual income to the same monthly basis. Do not compare a biweekly payment directly with monthly income.

Counting the whole condo fee in one view and half in another

Label the lender input and the household cash expense separately.

Ignoring revolving balances

The lender may impute a payment greater than the statement minimum. Update balances before approval and again before closing.

Treating gross rent as free income

Apply the lender's rental method and then run a vacancy, repair, and operating-cost model.

Spending the payoff money twice

Funds used to retire debt are unavailable for the down payment, land-transfer tax, legal costs, moving, and reserves. Reconcile cash with the closing-cost worksheet.

Treating 39% and 44% as a right

They are CMHC insured-underwriting limits described in its current guidance. The lender can decline, apply lower policy limits, or impose other conditions.

A decision table

Result	Likely issue	Useful next action
GDS high, TDS similar	Property carrying cost	Lower price/payment, tax, or fee burden
GDS passes, TDS high	Other debt	Verify inputs; retire debt with separate funds if sensible
Both high	Price/income mismatch	Reset price ceiling or wait
Ratios pass, cash flow fails	Gross-income illusion	Use lower household ceiling
Online result differs from lender	Input/policy mismatch	Request line-by-line reconciliation
Pre-approval passes, property fails	Property or updated file	Keep financing condition; review appraisal/documents

What to do next

1. Download current income, debt, property-tax, fee, and heating evidence.
2. Ask the mortgage professional for accepted inputs and the qualifying payment.
3. Reproduce GDS and TDS to two decimal places.
4. Identify whether GDS, TDS, cash to close, or appraisal is binding.
5. Build the after-tax ownership budget with full costs and reserves.
6. Test a rate increase, income interruption, and repair.
7. Set the offer ceiling from the lower of lender capacity and household capacity.
8. Keep a property-specific financing condition unless your lawyer and mortgage professional advise otherwise.

Frequently asked questions

What is a good GDS ratio in Canada?

CMHC's homebuying material uses 32% as a general affordability rule and describes 39% as its insured qualification limit. A suitable household target may be lower after accounting for tax, dependants, savings, variable income, and ownership costs omitted from GDS.

What is a good TDS ratio in Canada?

CMHC presents 40% as a general affordability rule and 44% as its insured qualification limit. Treat the higher number as an underwriting ceiling within the applicable program, not a recommended spending target.

Does GDS use the actual mortgage rate?

The qualifying payment can use a higher stress-test rate. Banks currently use the greater of 5.25% or the negotiated rate plus two percentage points for the federal mortgage stress test.

Are condo fees included in GDS?

CMHC's current professional guidance includes 50% of condominium fees in GDS and TDS. The household budget must include the full fee, and another lender or insurer's applicable policy should be confirmed.

How are credit cards counted in TDS?

CMHC says unsecured lines and credit cards should receive a monthly payment of no less than 3% of the outstanding balance in its calculation. Ask the lender which balance date and policy it used.

Can paying off a car loan improve mortgage qualification?

It can reduce recognized monthly debt if the lender accepts the payoff and evidence. Compare the ratio benefit with the loss of cash needed for the down payment, closing, and emergency reserves.

Does a mortgage pre-approval confirm my GDS and TDS for a home?

It confirms only the assumptions and file reviewed at that time. The actual property's tax, heat, condo fee, appraisal, condition, and lender eligibility can change the result.

Why does my lender calculate a different ratio from an online calculator?

Likely causes include accepted income, qualifying rate, amortization, insured premium, tax, heat, condo-fee percentage, debt payment, or rental-income method. Request each input and reconcile the difference line by line.

This article is educational and does not provide mortgage, legal, tax, accounting, or financial advice. Lending and insurer policies change and applications are assessed individually. Confirm current requirements and calculations with the lender, mortgage professional, insurer, lawyer, and tax adviser involved in your transaction.