Debt-to-income in one sentence
The CFPB defines debt-to-income (DTI) as all your monthly debt payments divided by your gross monthly income, meaning income before taxes and deductions. Its example: 1,500 mortgage + 100 auto + 400 other debts = 2,000 a month against 6,000 gross income, a DTI of 33%. The CFPB also notes that different loan products and lenders use different DTI limits, so there is no single correct threshold.
Two versions are in common use. A front-end or housing ratio counts only the housing payment. A back-end or total ratio counts housing plus every other debt payment: car loans, student loans, card minimums, personal loans. When a lender checks both, the stricter one sets your limit.
Real limits are lender rules, not a universal number
One published example is Fannie Mae's Selling Guide for conventional mortgages it buys. It sets a maximum total DTI of 36% of stable monthly income for manually underwritten loans, which can go up to 45% if credit score and reserve requirements are met, and up to 50% for loans underwritten through its Desktop Underwriter system. Its housing expense for a principal residence includes principal, interest, taxes, insurance and association dues. Car lenders, personal-loan lenders and banks outside the United States set their own limits, and those limits change. Treat any figure here as an example, and ask a lender for the ratio it will use.
A ceiling a lender will accept is not the same as a level you are comfortable with. DTI ignores childcare, groceries, transport, savings and taxes, since it starts from gross income. Many households choose a limit below the lender's maximum for that reason.
Worked example: from income to a loan amount
Gross monthly income is 6,000. Existing debt payments are 450 a month: a car loan and a card minimum. You choose a 36% total limit and look at a fixed 6.5% loan over 30 years.
| Step | Calculation | Result |
|---|---|---|
| Current DTI | 450 ÷ 6,000 | 7.5% |
| Total debt ceiling | 6,000 × 36% | 2,160.00 |
| Room for the new payment | 2,160 − 450 | 1,710.00 |
| Monthly rate and months | 6.5% ÷ 12; 30 × 12 | 0.5417%; 360 |
| Loan that 1,710 repays | 1,710 × (1 − 1.0054167^−360) ÷ 0.0054167 | 270,540.50 |
| Interest if repaid on schedule | 1,710 × 360 − 270,540.50 | 345,059.50 |
This is the loan-payment formula solved for principal. r is the monthly rate and N the number of payments. At 0% interest, P = M × N.
The mortgage correction: taxes, insurance and dues come first
Calculation Guide's affordability engine prices the whole 1,710 as principal and interest. That is right for a car or personal loan, and the Loan Payment calculator confirms that 270,540.50 at 6.5% for 30 years costs 1,710.00 a month. For a mortgage it overstates the loan, because lenders count the full housing payment, and property tax, insurance and dues take a slice of that 1,710 before any goes to the loan.
Say tax, insurance and HOA on the kind of home you want come to 450 a month. Handle that by adding 450 to the existing-debts field. The engine then leaves 1,260 for principal and interest, which supports 199,345.63, not 270,540.50.
Now check a housing-only limit too. If you also want housing at no more than 28% of income, the whole housing payment can be 1,680. Enter 450 as debts with a 28% cap: 1,230 is left for principal and interest, supporting 194,599.31. That is lower than the back-end result, so the front-end limit binds. Run both checks and take the smaller loan. Plugging 194,599.31 back into the Mortgage calculator with those costs gives 1,230 principal and interest and 1,680 total, which confirms the figures fit.
Mortgage CalculatorCheck that the modeled loan produces a full monthly housing cost you are comfortable with.How the limit and term change the answer
| Total DTI limit | Payment room | Modeled loan |
|---|---|---|
| 28% | 1,230 | 194,599.31 |
| 36% | 1,710 | 270,540.50 |
| 43% | 2,130 | 336,989.05 |
| 45% | 2,250 | 355,974.34 |
| 50% | 2,550 | 403,437.59 |
Every extra point of DTI adds 60 of payment room on this income, which supports roughly 9,500 more loan at 6.5% over 30 years. Term works the other way: at 36% over 15 years instead of 30, the same 1,710 supports 196,301.86, but total interest falls from 345,059.50 to 111,498.14. A longer term buys a larger loan by spreading it out, and the amortization schedule guide shows how much of that larger loan's early payments go to interest.
Limits of a DTI-based estimate
- It is not pre-approval. Credit history, employment stability, reserves, loan type and the lender's own counting rules decide the real figure.
- Which debts count varies. Lenders differ on how they treat deferred student loans, co-signed debts, alimony and debts with a few payments left. Enter what you expect your lender to count.
- Gross income hides taxes. Two people with the same gross income can have very different take-home pay. Check the payment against your actual monthly budget, not only the ratio.
- Fees and the down payment are outside the model. Closing costs, origination fees and the cash you need upfront limit what you can buy even when the ratio fits. Mortgage insurance on a low down payment also belongs in the monthly housing cost; see the PITI and PMI breakdown.