RATIOS
GDS and TDS, and why the income number is the higher one.
A lender does not ask what payment you can “afford” in the conversational sense. It asks whether stressed housing fits inside a ratio, and whether stressed housing plus your other debts fit inside a second ratio.
Gross debt service in this model is the stressed mortgage payment, plus property tax divided by twelve, plus a monthly heat figure, divided by gross monthly income. The cap used is 39%. Total debt service adds car payments, credit cards, and other monthly debts, and the cap used is 44%. The income you need is whichever cap demands more.
If you have no other debt, TDS is usually the looser test, because 44% is higher than 39% and the numerator is the same. A $400 car payment can flip it. The calculator shows both incomes and uses the larger. Many lenders will not go all the way to 39 and 44, especially on an uninsured file. Treat the result as the regulatory shape of the test, not as a pre-approval.
The payment inside the ratio is not the payment you will make. It is the payment at the qualifying rate. Read that page before you argue with the income figure.
Questions
Why is heat a separate input?
Lenders include a heating cost in housing. A default of about $100 a month is a placeholder, not your utility bill.
Do child-care costs count?
Some lenders count them in TDS. This calculator only has one box for other monthly debt. Put them there if you want them in the ratio.