The 28/36 rule is a classic guideline lenders use to gauge whether a mortgage payment fits your income. The two numbers are limits on your housing costs and your total debt as a share of gross monthly income. Knowing how these ratios work lets you estimate your borrowing power before you ever talk to a lender.
What the two numbers mean
The first number, 28, is the front-end ratio: your total monthly housing cost should not exceed 28% of gross monthly income. Housing cost here means PITI, the sum of principal, interest, property taxes, and homeowners insurance, plus any HOA dues or mortgage insurance. The second number, 36, is the back-end ratio: all your monthly debt payments, including the mortgage, should stay at or below 36% of gross income. Together they cap both your housing burden and your overall debt load.
How lenders apply it
Both ratios use gross income, meaning your pay before taxes and deductions, not your take-home. The back-end ratio adds obligations like car loans, student loans, minimum credit card payments, and child support to the proposed housing payment. Lenders compute both and generally require you to satisfy the stricter of the two for the program. Because the back-end ratio includes existing debt, paying down a car loan can directly increase how much mortgage you qualify for.
When lenders allow higher ratios
The 28/36 rule is a guideline, not a hard law, and many loan programs permit higher ratios. FHA loans, for example, often allow ratios around 31/43 and sometimes higher with compensating factors like strong reserves or an excellent credit score. Automated underwriting systems may approve back-end ratios in the mid-40s or even higher for well-qualified borrowers. Just because a lender allows a higher ratio does not mean stretching that far is wise for your budget.
Using the rule to plan
You can reverse the rule to estimate your target payment: multiply gross monthly income by 0.28 to see the housing budget the front-end ratio suggests. Then subtract existing debts from 36% of income to check the back-end limit, and use the smaller result. This quick math gives a realistic starting range before shopping. Remember that qualifying at the maximum ratio and living comfortably there are different things.
With $7,000 in gross monthly income, the 28% front-end limit is $1,960 for housing. The 36% back-end limit is $2,520 for all debt; if you already pay $500 toward a car and student loans, that leaves $2,020 for housing. The lender would use the lower figure, roughly $1,960, as your housing ceiling.
Key takeaways
- The front-end ratio caps housing costs at 28% of gross monthly income.
- The back-end ratio caps all debt payments at 36% of gross monthly income.
- Both ratios use gross income, and lenders usually enforce the stricter of the two.
- Programs like FHA often allow higher ratios, sometimes 43% or more with strong credit.
- Paying down other debts lowers your back-end ratio and can boost your borrowing power.
Common mistakes
- Using take-home pay instead of gross income, which understates the ratios lenders actually apply.
- Forgetting to include property taxes, insurance, and HOA dues in the front-end housing figure.
- Borrowing to the maximum allowed ratio and leaving no room for saving or surprises.
FAQ
Is the 28/36 rule mandatory?
No, it is a widely used guideline rather than a legal requirement. Many programs approve higher ratios, but the rule remains a useful sanity check on affordability.
Which ratio matters more?
Lenders generally require you to meet the stricter of the two, so whichever caps your payment lower is the binding one. For borrowers with existing debt, the back-end ratio often controls.