28/36 Rule Calculator
Calculate your housing affordability using the 28/36 rule. Find max mortgage payment, debt-to-income ratios, and how much house you can afford.
Enter your financial details and press Calculate to see your 28/36 rule analysis.
About
The 28/36 rule is a lending guideline used by most conventional mortgage underwriters in the United States. It states that a household should allocate no more than 28% of gross monthly income to total housing expenses (the front-end ratio, Rf) and no more than 36% to total debt service including housing (the back-end ratio, Rb). Exceeding either threshold increases default probability. Fannie Mae and Freddie Mac enforce these limits on conforming loans, though FHA permits ratios up to 31/43 and VA loans may waive front-end caps entirely. This calculator computes both ratios from your actual figures, reverse-calculates the maximum housing payment your income supports, and estimates the corresponding mortgage principal at a given interest rate.
Note: the rule assumes stable, documentable income. Irregular earnings (freelance, commission-heavy) require manual adjustment. Property tax and insurance are included in the front-end ratio per PITI convention. The tool does not account for private mortgage insurance (PMI), which applies when down payment falls below 20%. Pro tip: lenders may also apply a residual income test, so passing 28/36 alone does not guarantee approval.
Formulas
The front-end ratio measures housing burden relative to gross income:
The back-end ratio adds all recurring debt obligations:
Maximum affordable housing payment under the 28% rule:
Maximum total debt service under the 36% rule:
Remaining debt capacity after housing and existing obligations:
Estimated maximum mortgage principal from the affordable monthly payment, using the standard annuity formula:
Where: Rf = front-end ratio, Rb = back-end ratio, H = total monthly housing cost (PITI: principal, interest, taxes, insurance, HOA), D = total monthly non-housing debt payments, I = gross monthly income, M = affordable monthly mortgage payment (P&I portion of Hmax), r = monthly interest rate (annual rate ÷ 12), n = total number of payments (years × 12), P = maximum loan principal.
Reference Data
| Loan Program | Max Front-End Ratio (Rf) | Max Back-End Ratio (Rb) | Notes |
|---|---|---|---|
| Conventional (Fannie/Freddie) | 28% | 36% | Standard conforming guideline |
| Conventional (strong file) | 28% | 45% | Requires high credit score ≥ 740, reserves |
| FHA (Federal Housing Admin) | 31% | 43% | Allows lower credit scores, requires MIP |
| FHA (compensating factors) | 40% | 50% | Energy-efficient homes, large reserves |
| VA (Veterans Affairs) | No cap | 41% | Uses residual income test instead of front-end |
| USDA Rural Development | 29% | 41% | Income limits apply by county |
| Jumbo (non-conforming) | 28% | 36 - 43% | Lender-specific, stricter reserves |
| Qualified Mortgage (QM) | N/A | 43% | Dodd-Frank safe harbor threshold |
| Non-QM / Portfolio | Varies | 50%+ | Bank statement loans, asset depletion |
| Freddie Mac Home Possible | 28% | 43% | Low-income borrowers, ≤ 80% AMI |
| Fannie Mae HomeReady | 28% | 45% | Boarder income allowed, DU approval |
| Construction-to-Perm | 28% | 36% | Ratios based on completed-value appraisal |
| Physician / Doctor Loan | No cap | 45% | Excludes student loan IBR payments |
| Credit Union Portfolio | 30% | 40% | Member-specific underwriting |
| HFA (state housing agencies) | 30% | 45% | First-time buyer programs, DPA eligible |