Your debt-to-income ratio, DTI for short, is the share of each month's income already committed to repayments. The CFPB defines it as all your monthly debt payments divided by gross monthly income. With $5,000 a month before tax and $1,900 going on a mortgage, a car loan and card minimums, your DTI is 38%.
Lenders often split it in two. The front-end or housing ratio counts only the home: mortgage, property tax, insurance and any building charge. The back-end or total ratio adds every other debt payment on top. Canada names the pair formally: CMHC caps gross debt service at 39% and total debt service at 44% for a loan it insures, and counts a credit card at no less than 3% of the balance even if your minimum is lower. Japan's Flat 35 loans apply a similar total test, the 総返済負担率, which the Japan Housing Finance Agency sets at 30% of annual income below ¥4 million and 35% at or above it.
What counts as income differs too. American and Canadian rules use pay before tax, while several European lenders work from take-home pay, so the same household can show 30% in one country and 40% in another.
Do not confuse DTI with a cap on the size of the loan. New Zealand's Reserve Bank uses the same name for total debt divided by annual income, a multiple such as 6, which is closer to a loan-to-income ratio than to a share of monthly pay.
The debt-to-income calculator works out both ratios on the income basis your country uses, reads them against that country's own limits, and labels each limit as either a published rule or a lending convention.