You want to buy a house. The real estate agent says, "You can afford a $350,000 home." But how do they know? What mathematical rule determines how much you can borrow? The answer lies in a single metric: Debt to Income Ratio (DTI). Lenders don't just look at your salary. They look at your total monthly debt obligations compared to your gross monthly income . If you earn $5,000/month but owe $2,000/month on existing debts, you only have $3,000 left to pay a mortgage, car payment, or new loan. You could try to calculate this manually by listing all debts and dividing by income. But with multiple loans, varying payment amounts, and lender-specific rules, the math gets complicated. Or you could use a debt to income ratio calculator to instantly show that with a $75,000 annual salary and $1,500 in monthly debt payments, your DTI is 24%—which likely qualifies you for a mortgage, but not an additional car loan. A debt to income ratio calculator computes the percentage of your g...