DTI is your monthly debt obligations measured against your monthly income. It drives both whether you're approved and how much for.

It's calculated two ways. One compares only housing costs against income. The other adds every other debt on top. Programs weigh these differently, and the second figure is usually what governs approval.

What actually decides the outcome is less the ratio than how it was built. Certain debts drop out of the numerator under specific conditions — an installment loan with only a few payments left, a vehicle lease paid by an employer, an obligation a divorce decree assigns to someone else. Each has to be documented to be excluded.

The income side shifts by program too. For the same self-employed borrower, income measured from tax returns, from business bank deposits, and from profit-and-loss statements produce three different numbers. That's why the same file can yield different ratios depending on where it's reviewed.

A self-calculated DTI landing somewhere other than the underwritten number is the norm, not the exception. And a high ratio isn't automatically disqualifying — a larger down payment or strong reserves can offset it. Before any number goes into a calculator, we establish which income and which debts will actually count.