What Is a Total Debt Service Ratio Calculator?

A total debt service ratio calculator divides all of your monthly debt payments by your gross monthly income and expresses the result as a percentage — the number lenders use to decide how much debt you can safely carry. It comes in two forms. The Gross Debt Service (GDS) ratio counts housing costs alone: mortgage principal and interest, property taxes, heating and half of condo fees. The Total Debt Service (TDS) ratio adds every other obligation — car loans, student loans, credit cards, personal lines — and is the tougher test because it reflects your whole debt load rather than the mortgage line by itself.

The ratio matters because lending decisions are made against hard thresholds. In Canada the long-standing guidelines are 32% GDS and 40% TDS, with the federal stress test generally allowing up to 39% and 44%. In the United States, conventional lending often caps the back-end ratio near 36%, with automated approvals reaching 43% to 50% for strong credit. Knowing both ratios before you apply — and how much headroom you have under each limit — turns a binary approval decision into a modelling exercise you control.

How It Works

The calculator converts gross annual income to a monthly figure by dividing by twelve. It divides housing costs by that monthly income for the GDS ratio, and housing plus all other debt payments by the same income for the TDS ratio. It then works each limit in reverse: the maximum housing payment is income multiplied by the GDS limit, and the maximum total debt service is income multiplied by the TDS limit.

Subtracting your actual payments from those maximums produces headroom on both lines — the amount by which you are inside or outside the guideline. The remaining income figure is what is left of gross income after housing and debt payments, before tax and living costs. When a hypothetical purchase or refinance is on the table, re-running the numbers with the new payment shows immediately whether the ratios still clear the lender's thresholds.

Understanding Your Results

The primary card reports the TDS ratio with a pass or fail against both limits, and the GDS ratio beneath it. The three-stat bar shows the monthly income and the two payment components, while the breakdown table separates the housing contribution to GDS from the additional debt contribution that makes up TDS, so the two ratios are visible as parts of one picture.

Summary Statistics adds each ratio's standing against its limit, the maximum housing and total debt payments the income supports, and the headroom on both lines. Treat the limits you enter as policy inputs, not constants: lenders differ, insured and uninsured mortgages are treated differently, and the stress test rate changes with the market. The most reliable use of the calculator is to keep a buffer — if a payment clears the limit by a comfortable margin, a rate rise at renewal will not turn a qualified borrower into a strained one. Re-run the numbers after any rate change, income change or new loan, and keep the two ratios together — housing comfort and total debt capacity rarely move in the same direction at the same time.