GDS and TDS: The Two Debt-Service Ratios That Decide What You Qualify For

Most first-time buyers think their mortgage approval comes from one number — the maximum the bank says they can borrow. It comes from two. The bank runs your numbers through two separate debt-service ratios, and the lower of the two ceilings is what actually limits you.

Knowing which one binds for you tells you what to fix to qualify for more. If GDS is your constraint, you need a cheaper property or a bigger down payment. If TDS is your constraint, you need less other debt. Confusing the two — and trying to fix the wrong thing — is one of the more expensive mistakes we see at the pre-approval stage.

What this is, in plain English

Two ratios. The first one only counts housing costs. The second one counts everything.

Gross Debt Service (GDS) ratio is your monthly housing costs divided by your monthly gross household income, expressed as a percentage. Housing costs in the calculation include:

• Your stress-tested mortgage principal and interest payment (not your contract payment)
• Property taxes (use the actual amount from the city or BC Assessment)
• 50% of strata fees, if applicable
• A heating cost estimate, commonly $100/month for a condo or townhouse

CMHC caps GDS at 39% for insured mortgages. So if your gross household income is $130,000 — that's $10,833/month — your housing budget ceiling is $4,225/month before the bank flags GDS as the problem. (Run your own income through the home affordability calculator to see your specific GDS and TDS ceilings.)

Total Debt Service (TDS) ratio is GDS housing costs plus every other monthly debt payment, divided by gross household income. Other debts include:

• Car loans (use the monthly payment)
• Student loans (monthly payment)
• Credit card balances (3% of the balance is the standard calculation, regardless of what you actually pay)
• Personal lines of credit (use the monthly minimum)
• HELOCs — fully drawn, even if unused (more on this below)
• Spousal or child support obligations

CMHC caps TDS at 44%. Same household earning $10,833/month: total monthly debt commitments (housing plus everything else) can't exceed $4,766.

The bank checks both. The lower ceiling is your approval.

How it actually works for a Fraser Valley first-time buyer

A worked example, since the abstractions don't really make sense until you see the numbers move.

Couple buying their first home together. Combined gross household income: $130,000/year ($10,833/month). No kids yet. Looking at a $650,000 Willoughby townhouse with a 10% down payment ($65,000), 30-year amortization, stress-tested at 6.5%.

Mortgage: $585,000 at 6.5% stress-tested over 30 years = roughly $3,690/month Property tax: ~$280/month (typical for a $650K Langley townhouse, per BC Assessment-style estimates) Strata fees: $290/month — half counted = $145 Heating: $100/month

GDS housing costs total: $4,215/month GDS ratio: $4,215 ÷ $10,833 = 38.9% — just under the 39% ceiling

So they qualify on GDS. Now check TDS.

Other monthly debt:

• One car loan: $385/month
• A line of credit with $8,000 balance: 3% of balance = $240/month
• No student loans, no credit card balances carried month-to-month

TDS total: $4,215 + $385 + $240 = $4,840/month TDS ratio: $4,840 ÷ $10,833 = 44.7% — over the 44% cap

They fail on TDS by about $74/month. The bank says no — not because they can't afford the housing, but because the other debt pushes them past the total-debt ceiling.

What fixes it? Three real options. They pay down the line of credit to drop the calculated payment. They wait to buy until the car loan is paid off. Or they look at a cheaper property — about $635,000 — where the lower mortgage payment gives back the $74 of TDS room.

The takeaway: TDS bound this purchase, not GDS. The right fix is the debt side, not the property side. A lot of buyers in this position try to negotiate harder on the listing price when what they actually need is to wait three months and pay off the car.

What changes the answer

A handful of variables move which ratio binds:

No other debt. GDS usually binds first. You're competing against the 39% housing-to-income ceiling, which means the lever is either bigger down payment or cheaper property.

Significant car payment, student loans, or credit card balances. TDS binds first. The lever is paying down or paying off other debt — the housing side is fine.

Self-employed income. Lenders typically average your last two years of Line 15000 from your T1 General, sometimes with a 15% gross-up if you can show the income is consistent and the deductions are documentable. Some lenders take a haircut instead. This shrinks the income side of both ratios.

Co-borrower with no income. A spouse who isn't on title doesn't add to the income side. If they're carrying the debts (car loan in their name only, for example), the debt doesn't count either. If they're on title, their income and their debt both count.

Heating estimate. Most lenders default to $100/month for a condo or townhouse. Detached homes get $150-$175. If your actual heating bill is meaningfully higher (older building, electric baseboards), some lenders will use the actual number if you can show it.

Property tax estimate. Use the actual property tax from the listing's recent assessment if you have it, or check BC Assessment for the property. Estimating low and being surprised after the fact is one of the more common GDS misses we see.

The HELOC trap

This is the line item that catches more first-time buyers off-guard than any other.

A Home Equity Line of Credit on a previous property, or a credit-card-style line of credit you opened years ago and never used — the bank treats it as if it's fully drawn at the stress-test rate, amortized over 25 years. A $50,000 HELOC limit you've never touched generates a stress-tested payment around $330/month in the TDS calculation. A $100,000 limit generates around $660/month.

That's $660 of TDS room you don't have, on debt you don't owe.

The fix is to close any unused HELOCs and personal lines of credit before you apply for the mortgage. Don't just pay them down to zero — close them, get a confirmation letter from the lender, and have it ready for your mortgage broker. We've seen $80,000–$120,000 of qualifying mortgage appear after this single step.

Same logic applies to credit card limits. If you have a card with a $25,000 limit and no balance, 3% of the limit ($750/month) doesn't get counted as TDS debt unless the balance is positive. But if you carry a $1,000 balance, the 3% calculation kicks in. Pay your cards to zero before the application and the calculation drops.

Common mistakes we see

Estimating property tax low. A new build in Surrey or Langley has a tax estimate that's often based on the construction value during the assessment year, not the completed home. The first-year tax bill shows up at the actual value and the GDS ratio you qualified on is suddenly out of date. Ask your realtor for the current owner's tax bill — that's the number to model.

Ignoring strata fees in the math. "It's a townhouse, the strata fee is low" — except half of $250/month is $125 added to GDS. On a marginal qualifying application, $125 is the difference between approval and denial.

Treating a co-signer as a free option. Co-signers with their own debt and their own housing costs can actually reduce your qualifying mortgage if their TDS is worse than yours. The lender doesn't just average the incomes — they re-run both ratios with everyone's debt loaded in.

Submitting with old credit-card balances. Your credit-card balance on the day the lender pulls credit is what they use for the 3%-of-balance calculation. If you put a $4,000 ski trip on a card the month before you apply, that's $120/month of TDS counted against you. Pay it off, wait for the next statement cycle to update, then apply.

Forgetting that the qualifying rate is not the contract rate. Both ratios use the stress-tested payment, not the payment you'll actually make. At a 4.5% contract rate stress-tested to 6.5%, the difference between contract payment and qualifying payment on a $500K mortgage is about $570/month. The bank checks the higher one.

Where this fits in the bigger picture

GDS and TDS are the floor under the stress test — the test calculates the payment, the ratios decide whether you fit underneath it. They also decide whether the insured vs uninsured choice matters in practice (insured has stricter ratio caps), and how much the broker vs bank channel choice can stretch you (some monoline lenders accessed through brokers will go to slightly higher ratios than a bank branch).

Read the pillar page for the full affordability map, the stress test deep-dive for what the qualifying rate does to the payment side, or the pre-approval vs approval page for the gap between a pre-approval letter and a funded mortgage on offer day.

Sources

• CMHC — Mortgage affordability calculator
• OSFI — Minimum qualifying rate for uninsured mortgages
• Bank of Canada — Policy interest rate

More in this hub

• How much house can you actually afford? (pillar)
• Fixed vs variable mortgages in BC
• Insured vs uninsured mortgages
• Mortgage broker vs bank — who to call first

Want help running these numbers on your actual situation? Book a 20-minute chat with the FRIVE team — we'll walk you through what each ratio looks like for your income and which lever moves the needle.

Where to go next

• Mortgage stress test 2026 — the qualifying rate that feeds into the GDS/TDS calculations
• Condos for sale in Surrey, BC — strata fees are a GDS input; here's what they actually look like in Surrey
• Townhomes for sale in Surrey, BC — townhouse strata fees and pricing in Clayton, Fleetwood, and Newton
• Townhomes for sale in Langley, BC — how Langley's benchmark interacts with income qualifying at current rates