Gross Debt Service (GDS)

GDS = qualifying housing costs ÷ gross qualifying income × 100. The glossary definition is at Gross Debt Service ratio (GDS).

For a typical owner-occupied mortgage, the housing-cost side includes the qualifying mortgage principal-and-interest payment, property taxes, heating and the applicable portion of condo/site/other housing fees under the program. Other consumer debts do not belong in GDS; they enter TDS.

Use the Maximum Mortgage Calculator immediately after the formula if your real question is 'What mortgage amount fits my GDS?'

Before GDS is calculated, the lender has already chosen the qualifying income, rental method and stress-test payment. A difference in any one of those inputs can move the ratio even though the formula itself never changes.

That is why the practical sequence is How Lenders Calculate Income → How Lenders Calculate Rental Income → Mortgage Stress Test Math → GDS.

Qualifying annual income is $150,000, or $12,500 per month. Qualifying mortgage payment is $3,500, property tax $600, heat $150 and the applicable counted portion of condo fees is $150. Total GDS housing costs are $4,400.

$4,400 ÷ $12,500 = 35.2% GDS. Paying off a credit card would not change this ratio because the card is a TDS debt. Increasing accepted income or lowering the qualifying mortgage payment would.

For mortgage loans that must meet the federal insured/insurable eligibility criteria, GDS must not exceed 39% and TDS must not exceed 44%. This is why an insured deal is fundamentally different from a conventional lender exception: the lender cannot simply decide that 45% GDS is acceptable and still treat the mortgage as if it satisfied the applicable insured eligibility framework.

The insurer still has product-specific rules for income, rent, debts, property and documentation. The 39% maximum is only one part of the insured approval.

Conventional uninsured files do not all share one hard 39/44 ceiling. The lender applies its own policy and exception authority, usually looking at factors such as credit quality, down payment/equity, income stability, liquidity, property, loan purpose and the size of the exception.

HopeWell broker-channel observations — August 2026: Scotiabank has considered conventional files around 50/50; TD commonly has room around 47/47 in suitable cases and HopeWell has had one TD file accepted at approximately 48/48. B2B Bank has also shown ratio flexibility when the overall file fits its equity/net-worth programs. Many prime monoline lenders are generally stricter on extended ratios even when the mortgage is conventional.

Those numbers are not published promises. They are examples of how lender fit changes the result and must be reconfirmed on the live application.

In HopeWell's alternative-lender work, 50/50 is a common starting range. But B lending is not one policy. Equitable Bank currently publishes 50/50 standard and 60/60 in select markets on its alternative BFS program. Home Trust publicly shows a funded example at 60% TDS. B2B Bank's Net Worth Program currently publishes 70% TDS with higher potentially considered by exception for that product.

These examples show the width of the alternative channel, not that every B lender will approve 60% or 70% ratios. Credit, LTV, location, property type, income method and program all matter.

Private lenders generally place more weight on property value, equity, loan position and the exit plan than on bank-style debt-service ceilings. Yet affordability still matters: bank statements and income evidence help show whether the borrower can carry the interest and protect the equity during the private term.

HopeWell therefore calculates the institutional ratios anyway when the exit is supposed to be an A or B refinance. A private mortgage that ignores today's high TDS without a plan to improve it can create a maturity problem later.

Depending on the lender/insurer method, accepted rent can increase the income denominator, offset subject-property housing costs, or enter a separate property worksheet. Some methods also alter which taxes/heat/property costs remain in the numerator.

Do not add a rent percentage to salary and assume the job is done. Use How Lenders Calculate Rental Income before calculating the ratio.

GDS uses gross qualifying income, not take-home pay. It does not account for every real cost of living, such as childcare, food, transportation, income tax, insurance, repairs or savings goals.

Treat it as an underwriting ratio, then run a separate household cash-flow test before deciding how much of the approved mortgage to use.

If qualifying monthly income is $12,500 and the applicable GDS ceiling is 39%, total qualifying housing cost cannot exceed $4,875 per month. Deduct property tax, heat and applicable fees; the remainder is the mortgage-payment allowance.

That payment allowance can then be converted into mortgage principal using the qualifying rate and amortization. The Maximum Mortgage Calculator automates the complete chain and also checks TDS, which may be the tighter constraint.