House Affordability Calculator · Practical guide
What Is the 28/36 Rule for Mortgages?
Front-end 28%, back-end 36%: how the two caps work, which one binds, and worked examples by income and debt.
At a glance
The Rule in One Sentence
The 28/36 rule says housing costs should not exceed 28% of your gross monthly income, and housing plus all other debt payments should not exceed 36%. Lenders have used it for decades as the baseline mortgage-qualification guideline.
Interactive tool
House Affordability Calculator
Enter your own values, then compare the result with the examples below.
Front-End vs Back-End
- Front-end (28%): principal, interest, taxes, and insurance (PITI) divided by gross monthly income.
- Back-end (36%): PITI plus car loans, student loans, and credit card minimums divided by gross monthly income.
Your maximum housing payment is whichever cap binds first: min(0.28 x income, 0.36 x income - monthly debt).
Worked Example
Earning $90,000 a year ($7,500 a month) with $400 of monthly debt: the front-end cap is 0.28 x $7,500 = $2,100; the back-end cap is 0.36 x $7,500 - $400 = $2,300. The 28% cap binds, so $2,100 is the most you should spend on housing — enough for about a $336,000 home with 20% down at 6.5%.
Where the 36% Cap Bites
Debt above roughly 8% of gross income flips the binding constraint. On $7,500 a month, once other debts pass $600, the back-end cap takes over: at $1,200 of debt the housing allowance falls to $1,500 — cutting the affordable price by roughly 30%.
Frequently Asked Questions
Is the 28/36 rule a law?
No. It is a conservative guideline. Many loan programs allow higher ratios — FHA up to 31/43, and conventional loans up to 45-50% back-end through automated underwriting.
Does the rule use gross or net income?
Gross (pre-tax) income, the same figure lenders use when qualifying you.
What counts as housing cost in the 28%?
Principal, interest, property taxes, and homeowners insurance — PITI. Lenders often include HOA dues and PMI as well.
Is 28/36 still realistic with today's prices?
It is intentionally conservative. Many buyers stretch to 36/43, but staying near 28/36 leaves room for savings, maintenance, and surprises.