25% housing and 40% total — the second is what fails the 28/36 test
The front-end ratio is housing against gross income: $1,500 on $6,000 is 25%. The back-end ratio adds every other required monthly payment — $400 of car, $300 of student loan, $200 of card minimums — for a total of $2,400, or 40%. The classic underwriting guideline allows 28% and 36%, so this household clears the housing test comfortably and fails the overall one by four points.
Front-End DTI = Housing ÷ Gross Income × 100 | Back-End DTI = All Debts ÷ Gross Income × 100
That pattern is the common one. Housing is the largest single payment and the one buyers focus on, while the ratio that actually constrains approval is the one counting the car and the cards. It also points at the fix: eliminating the $400 car payment takes the back-end ratio from 40% to 33.3% and brings the file inside the guideline without touching the mortgage at all.
Minimum payments count in full; utilities and groceries do not count at all
Lenders count required monthly debt obligations: mortgage or rent including taxes and insurance, car loans and leases, student loan payments, credit card minimums, personal loans, and court-ordered payments such as alimony or child support. Only the minimum counts on a card, however much you actually pay.
Living costs are excluded entirely — utilities, phone, groceries, insurance premiums that are not part of housing, childcare, and retirement contributions. This is why a household can pass a debt-to-income test and still be stretched: the ratio measures obligations a lender can enforce, not the cost of living. It is a lending screen, not a budget.
$6,000 gross is roughly $4,650 in hand, which makes 40% of gross nearer 52% of take-home
Debt-to-income uses gross, pre-tax income. For a typical US household, take-home might be around 75–80% of gross once federal and state tax, Social Security, Medicare, health premiums and retirement contributions come out. So a back-end ratio of 40% of gross is closer to half of the money actually arriving in the account.
That gap is why the guideline ratios feel tighter in practice than they look on paper, and why a household at the edge of the limit often finds the payment uncomfortable even though it was approved. Running the same debts against your net pay is a useful private check alongside the figure a lender will compute.
Clearing a small high-payment loan beats paying down a large low-payment one
Because the ratio counts payments rather than balances, the efficient move is to eliminate whichever debt carries the largest monthly payment relative to its remaining balance. A car loan with $5,000 left and a $400 payment removes 6.7 points of back-end ratio; $5,000 paid against a mortgage removes almost nothing, because the payment barely changes.
The other side is income, which lenders will only count if it is documented and stable — typically two years of history for self-employment, bonus or commission income. Raising the denominator works, but it works on the lender’s terms rather than on the last three months of earnings.
Many loan programmes allow far higher ratios than this test implies
The 28/36 rule is a conservative convention, not a universal standard. Fannie Mae’s Selling Guide caps back-end DTI at 36% for a manually underwritten loan, 45% with a strong credit score and reserves, and 50% through its Desktop Underwriter; FHA loans can go higher with compensating factors. Failing the guideline here does not mean failing an application.
The calculation also assumes the housing figure you enter is the full PITI — principal, interest, taxes and insurance, plus mortgage insurance and any HOA dues. Entering principal and interest alone understates the front-end ratio substantially, often by several points on a property with high taxes.
Frequently Asked Questions
What is the maximum DTI for a mortgage?
For a conventional loan sold to Fannie Mae the cap is 36% when underwritten by hand, 45% with a strong credit score and reserves, and 50% through Desktop Underwriter (Selling Guide B3-6-02). FHA loans can go above 43% with compensating factors, VA loans treat 41% as a guideline rather than a hard cap, and jumbo lenders set their own, often stricter, limits.
Should I include current rent in my DTI?
For a new mortgage application, use the proposed mortgage payment (PITI), not your current rent. Rent is not a debt — it disappears when you buy. Lenders substitute the proposed mortgage payment instead.
How can I lower my DTI?
Either increase income or reduce monthly debt. Paying off a car loan or student loan before applying for a mortgage meaningfully reduces back-end DTI. A larger down payment reduces monthly mortgage payment and front-end DTI.
What is the difference between front-end and back-end DTI?
Front-end DTI counts only your housing payment against gross income and is often capped near 28%. Back-end DTI counts all recurring debt payments, including housing, and is the figure lenders cap: 36% to 50% for a conventional loan, depending on how it is underwritten. This calculator shows both so you can see which one is the binding constraint.
Sources & References
Figures on this page are checked against primary, authoritative sources. Links open in a new tab.
Income is gross (pre-tax) monthly income, not take-home pay.
Housing payment includes all PITI components for mortgage applications.
Credit card debt uses minimum required payments, not full balances.
Where it stops
Different loan programs have different DTI limits. FHA allows up to 50% back-end DTI with compensating factors.
Lenders also weigh credit score, assets, and employment history — DTI alone does not guarantee approval.
Self-employment income is calculated differently by lenders (typically 2-year average net income).
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Results are estimates based on the figures you enter and standard formulas. Rates, fees, taxes, and lender terms vary and change over time, so confirm important numbers with your lender or a qualified professional. This is educational information, not financial advice.
Restored this calculator to the catalog. It had been retired as a deletion rather than merged into another tool, so unlike the merged slugs no surviving calculator covered debt-to-income; the URL now serves a full page again and the legacy /budget/ path redirects to it.
Published the calculator with its formula, worked example, assumptions, limitations and FAQs, and added an automated formula test suite covering it.
Property-tested that the gap between the front-end and back-end ratios is exactly non-housing debt over income.
Replaced the 43% back-end limit, the old Qualified Mortgage cap, with Fannie Mae's Selling Guide limits (36% manual, 45% with credit score and reserves, 50% through Desktop Underwriter) and added that source.
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