GDS, or gross debt service
The share of your gross income going to housing costs: the mortgage payment calculated at the qualifying rate, municipal and school taxes, heating, and a portion of condo fees where they exist. The result is expressed as a percentage of income.
TDS, or total debt service
The same calculation plus every other obligation: car loan, student loan, card payments, lines of credit, support payments. This is the ratio that most often stops a file.
The thresholds applied
Lenders and insurers work to customary caps on each ratio, with wider tolerance when the credit file is strong. These caps are policies and get revised: ask the target lender for the thresholds in force.
Available credit counts, not just used
A line of credit or card is often costed at a theoretical minimum payment, even at a zero balance. A high limit you never touch can therefore cut your borrowing capacity.
What counts as income
A regular salary counts in full; variable income, commissions, self-employment, or rental income are weighted, averaged over several years, or only partly recognized. Two people reporting the same income do not have the same capacity.
The fastest lever
Paying off or closing a small debt with a high monthly payment improves TDS faster than a bigger down payment. Have both ratios calculated before deciding where to put your cash.
No rate, price, or recommendation on this page. Amounts and limits change: verify them with official sources before deciding.