The 28/36 guideline: housing costs should be ≤28% and total debt ≤36% of gross monthly income.
The 28/36 Rule: Front-End Ratio = Housing Cost / Gross Income ≤ 28% Back-End Ratio = (Housing + All Debts) / Gross Income ≤ 36%
The 28/36 rule is not a federal regulation. It is an underwriting heritage — a pair of ratios baked into the Fannie Mae and Freddie Mac selling guides decades ago and adopted by virtually every conventional lender since. Hitting both numbers gets you to "easy approval." Missing them is a signal to either pay down debt, buy less house, or shop a loan program with more permissive ratios.
Where the rule came from
The split into two ratios — housing alone versus housing plus all other debt — dates to the 1970s when Fannie Mae standardized conventional mortgage underwriting. The percentages were calibrated to the average American household's typical spending on food, utilities, transportation, and savings at that time. Despite the dramatic increase in housing costs since, the same ratios still anchor the U.S. mortgage market.
Front-end (28%) vs back-end (36%) — what counts in each
Front-end (28%) — housing only. Principal and interest, property taxes (escrowed), homeowners insurance, HOA dues, and mortgage insurance (PMI if applicable) all sum into the numerator. Utilities, maintenance, and reserves are not counted.
Back-end (36%) — housing plus all other debt service. Add minimum credit-card payments, auto loans, student loans, personal loans, child support, alimony, and any other recurring debt that appears on your credit report.
What's not in either: retirement contributions, daycare, groceries, gasoline, subscription services. These are excluded because they're personal-budget choices, not contractual debt — but they still need to fit in the remaining 64% of your income.
Walkthrough: $8,000 gross monthly income
Maximum housing payment (28%) = $8,000 × 0.28 = $2,240 per month
Maximum total debt service (36%) = $8,000 × 0.36 = $2,880 per month
Available capacity for non-housing debt: $2,880 − $2,240 = $640 per month
If existing car + student-loan + credit-card minimums total $500: remaining housing capacity is $2,880 − $500 = $2,380, but capped by the front-end at $2,240.
If existing debts total $900: remaining housing capacity drops to $2,880 − $900 = $1,980, which is now your binding constraint.
When the rule bends — loan-program overrides
FHA loans: 31% front-end and 43% back-end as standard caps, with manual underwriting going to 40/50 in strong files.
VA loans: No strict front-end limit; 41% back-end target plus a residual-income test that varies by household size and region.
USDA Rural Development: 29% front-end and 41% back-end, with exceptions to 32/44 for strong credit.
Jumbo (non-conforming): Tighter, not looser — many jumbo lenders cap back-end at 38% to 43% even for prime borrowers.
Non-QM (non-qualified mortgage): Variable; bank-statement programs and asset-depletion loans use different qualifying frameworks entirely.
Compensating factors that allow exceptions
Underwriters can push past 28/36 when the rest of the file is unusually strong. Standard compensating factors include:
FICO score of 760 or above
Down payment of 20% or more on conventional, or 10%+ on FHA
Six or more months of mortgage payments in cash reserves
Stable employment with the same employer for 2+ years
Documented history of comfortable affordability of similar payment levels (rent close to the proposed mortgage)
Five ways to hit the limits before applying
Pay off the smallest revolving balance. A $5,000 credit card balance with a $150 minimum payment, when cleared, lifts back-end capacity by $150.
Refinance a high-payment auto loan to a longer term temporarily — the lower monthly payment shrinks the debt service numerator.
Add a qualifying co-borrower (typically a spouse or parent) whose income is added to the denominator and whose credit is also reviewed.
Increase the down payment. A larger down payment shrinks the loan amount and the monthly P&I, directly lowering the front-end ratio.
Buy in a lower-tax jurisdiction or with lower HOA fees. Tax and HOA flow into the front-end numerator just like principal and interest.
Frequently asked questions
Is the 28/36 rule the same as the qualified mortgage rule?
No, but they overlap. The Qualified Mortgage rule (CFPB, 2014) caps back-end DTI at 43% for most conforming loans — looser than the 36% guideline but still firm. The 28/36 rule is best practice; QM is the federal floor.
Why is the back-end ratio higher than front-end?
Because back-end includes housing already plus everything else. The 8-point spread (36 − 28) is the room a typical borrower has for car payments, student loans, and credit-card minimums in addition to the mortgage.
Does the rule apply to refinances?
Yes — refinance underwriting uses the same DTI standards as purchase underwriting in most loan programs, with some exceptions for streamline refinances (FHA Streamline, VA IRRRL, HARP successors).
What about self-employed income?
Lenders typically average the last 2 years of Schedule C net income, sometimes with add-backs for depreciation. Conservative lenders use the lower of the two years. The DTI calculation then proceeds normally with this adjusted gross income.
Should I use this calculator before house-hunting?
Absolutely. Knowing your DTI envelope before talking to lenders lets you negotiate from a position of knowledge and avoid falling in love with houses outside your affordability range.
Is rent counted in back-end DTI?
No — current rent is replaced by the new proposed mortgage payment for the purpose of the calculation. The assumption is that you won't be paying both at once.