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Scan for outdated or missing drivers - takes under a minuteDriver Scan →Clear out junk files and repair common Windows errorsFree Scan →The 28/36 rule is a U.S. mortgage budgeting guideline: aim to keep monthly housing costs at or below 28% of gross income, and monthly debt at or below 36% of net income. It is a starting estimate—not a lender’s standard debt-to-income (DTI) calculation or a universal mortgage-approval cutoff.
How the 28/36 rule works
Fannie Mae describes the 28% guideline as a way to estimate a manageable monthly mortgage expense: multiply gross monthly income by 0.28. The 36% guideline compares monthly debt with net monthly income. The debt figure includes the mortgage, car payments, credit-card debt and loan payments, but not utilities. Fannie Mae cautions that the figures are for a general idea of affordability, because many factors affect what a household can afford. Fannie Mae’s consumer guide presents these as rules of thumb, not approval requirements.
Calculate the 28% housing guideline
Start with gross monthly income—income before taxes and other deductions—and multiply it by 0.28. For example, if gross household income is $8,000 a month, the calculation is $8,000 × 0.28 = $2,240. That is a rough monthly housing-cost target under this guideline, not a promise that a particular mortgage payment will be affordable or approved.
Calculate the 36% debt guideline
For the consumer rule, compare the household’s monthly debt payments with net monthly income, meaning take-home income after deductions. The 36% figure is the suggested upper share for monthly debt, including the mortgage and other stated debt payments. Do not treat that calculation as equivalent to the DTI a lender will use: lender underwriting generally calculates DTI using qualifying gross income and obligations defined by the loan rules.
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Why a lender’s DTI calculation is different
Fannie Mae defines DTI as total monthly obligations divided by the total monthly income of borrowers whose income is used to qualify. Its calculation includes the qualifying mortgage payment and other long-term and significant short-term debts. The housing obligation can include principal, interest, taxes, insurance and assessments (PITIA), along with any applicable qualifying payment amount. Other obligations can include installment and mortgage debt, revolving accounts, leases, certain alimony or child-support payments, recurring monthly obligations and net rental losses. Some small short-term debts may count if they materially affect the borrower’s ability to meet obligations. See Fannie Mae’s Selling Guide DTI guidance.
The lender’s DTI is not a complete household budget. Fannie Mae’s liability guidance identifies obligations such as leases, real-estate loans, HELOCs, alimony and child support, maintenance payments and other recurring debts. It does not treat items such as taxes, FICA, some retirement contributions, commuting costs, union dues and voluntary deductions as liabilities in that DTI calculation. Those costs still affect how much money a household has available, so account for them when deciding what payment is sustainable. Fannie Mae’s monthly debt-obligations guidance explains which liabilities it examines.
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Why 36% is not a universal approval cutoff
The 36% figure has two distinct uses: it appears in the consumer rule of thumb, and it is also Fannie Mae’s general maximum DTI for manually underwritten loans. Under Fannie Mae’s guide, the manual-underwriting maximum may rise to 45% when specified credit-score and reserve requirements are met. For loan casefiles underwritten through Desktop Underwriter, Fannie Mae allows a maximum DTI of 50%. These are Fannie Mae underwriting rules, not limits that apply to every lender or mortgage program. The applicable requirements depend on the loan and underwriting path. Fannie Mae’s current DTI guidance sets out those thresholds.
Federal ability-to-repay rules do not establish one DTI ratio that all creditors must use. Regulation Z requires creditors to consider DTI or residual income as part of the ability-to-repay assessment, while allowing consideration of other factors such as assets and residual income. A consumer guideline or one agency’s underwriting limit therefore cannot determine approval on its own. See the CFPB’s Regulation Z, 12 CFR § 1026.43.
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- DEDICATED BUYER QUALIFYING KEYS: Enter client's income, debt and expenses to pre-qualify them to only show properties they can afford. Include tax, insurance and mortgage insurance then compare loan options and payment solutions to give your client choices before they make an offer to buy
- FIGURE OUT THE RIGHT LOAN: At the press of a button for jumbo, conventional, FHA/VA, or even 80:10:10 or 80:15:5 combo loans; check to see if ARMs or bi-weekly loans, quarterly payments or if interest-only payments are the answer; giving your client more choices; easily perform what if loan or tvm calculations Find loan amount, term, interest or PITI or PI payments
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How to use the rule when planning to buy
- Estimate a housing target. Convert gross annual income to gross monthly income, then multiply by 0.28. Treat the result as an initial monthly housing guideline.
- List current monthly debts. Compare them with the consumer rule’s 36% of net-income guideline, but remember that a lender generally uses qualifying gross income and lender-defined obligations for formal DTI.
- Budget for costs beyond the mortgage payment. Include down payment, property taxes, insurance, maintenance and fees. Also account for utilities and other regular household costs that may not appear in a lender’s DTI calculation.
- Refine the estimate. Use an affordability calculator and discuss prequalification with a lender to understand how your income, debts, assets, documentation and loan program affect the numbers. Fannie Mae also offers a free homebuyer education course through its homebuyer resources.
Fannie Mae’s consumer percentages are from its 2022 guide; the underwriting figures above are from its Selling Guide dated April 2, 2025. Regulation Z is cited from the CFPB’s January 1, 2024 annual-edition text.
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- DEDICATED BUYER QUALIFYING KEYS: Enter client's income, debt and expenses to pre-qualify them to only show properties they can afford. Include tax, insurance and mortgage insurance then compare loan options and payment solutions to give your client choices before they make an offer to buy
- FIGURE OUT THE RIGHT LOAN: For your client at the press of a button for jumbo, conventional, FHA/VA, or even 80:10:10 or 80:15:5 combo loans; check to see if ARMs or bi-weekly loans, quarterly payments or if interest-only payments are the answer; giving your client more choices; easily perform what if loan or TVM calculations find loan amount, term, interest or PITI or PI payments
- BECOME AN INVALUABLE RESOURCE: To your clients by reducing their confusion and uncertainty; ensuring they are able to make a purchase offer; knowing they can afford the down payment; and determining which is the right loan for them. Date-math for listings and contracts too. Comes with a protective slide cover, quick reference guide, pocket user's guide, and long-life battery
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