The debt-to-income ratio, or DTI, is one of the very few numbers a bank literally computes before deciding whether to approve your mortgage, personal loan or even an increase in your credit-card limit. It is a simple way of summarizing how much of your monthly income is already committed to repaying debt.
The formula
The formula is straightforward: DTI = (monthly debt payments / gross monthly income) × 100. Debt payments include everything on your credit report: mortgage or rent, personal loans, auto financing, credit-card minimum payments, alimony, student loans and any other recurring obligation.
Example
With gross monthly income of $6,000 and payments of: mortgage $1,700, car loan $420, credit-card minimum $80. Total $2,200. DTI = 2,200 / 6,000 = 36.7%. That tells the lender that for every dollar you earn, about 37 cents is already committed to debt.
Thresholds lenders use
- Under 28%: very comfortable. Almost any lender will approve additional credit if the rest of your profile is healthy.
- 28% to 36%: standard band. The typical range US and European lenders target for a conventional mortgage.
- 36% to 43%: borderline. Many lenders still approve, but may ask for cosigners, larger down payments, higher rates, or a shorter term.
- Above 43%: risk zone. In the US, the Qualified Mortgage standard uses 43% as a soft ceiling. Approval above that usually requires strong compensating factors like large reserves.
Front-end vs back-end DTI
Lenders usually look at two numbers. The front-end DTI (housing ratio) counts only housing costs: mortgage, insurance and property tax. The back-end DTI counts every debt. Front-end is typically kept below 28%; back-end below 36%.
Common mistakes when computing it
- Using net income instead of gross. Gross is the banking standard; net inflates the ratio artificially.
- Forgetting the new mortgage. When applying for a mortgage, use the future housing payment, not your current rent.
- Only counting what you actually pay on cards. Lenders use the minimum required payment, not whatever you voluntarily send.
- Excluding cosigned loans. If you cosigned a loan for someone else, that debt counts on your DTI too.
How to improve your DTI
There are two levers: reduce the numerator (debt payments) or grow the denominator (income). In the short term, the first one is more realistic. Concentrate extra payments on small balances to remove them from the ratio; use the debt payoff calculator to simulate how many months you need to clear each. Closing a card with an $80 minimum can lower your DTI by 1–2 points, enough to move from "borderline" to "standard".
DTI before applying for a mortgage
If a mortgage is the goal, start shaping your DTI 6–12 months in advance. Avoid opening new lines of credit, do not finance cars or appliances, and check that minimum payments are correctly reported. A DTI under 30% gives you room not just to be approved but to negotiate a better rate.
DTI vs true affordability
Meeting the lender threshold does not mean the deal is right for you. A 40% DTI can be mathematically approvable but leaves very little cushion for surprises, rate resets or income changes. Treat DTI as the formal minimum; your personal comfort threshold should be more conservative, especially if you are self-employed or have variable income.