Where the 28/36 rule comes from
The 28/36 rule has been used by mortgage lenders for decades as a quick, conservative way to gauge how much housing payment a borrower can reasonably handle without becoming financially overextended. It splits your budget into two checks — a housing-only cap (28%) and a total-debt cap (36%) — and your true limit is whichever one is more restrictive. The rule predates modern automated underwriting, but lenders still lean on it as a sanity check even when their software allows higher ratios.
Front-end vs. back-end, in practice
The "28" is your front-end ratio: housing costs alone (principal, interest, taxes, insurance, PMI, and HOA dues) divided by your gross monthly income. The "36" is your back-end ratio: that same housing payment plus every other recurring debt — car loans, student loans, minimum credit card payments — divided by gross income. You can pass the 28% test comfortably and still be capped by the 36% test if you're carrying meaningful other debt, which is exactly the scenario this calculator flags for you.
A worked example
Say you earn $6,000/month gross and pay $500/month toward a car loan and student loans. Your 28% housing cap is $1,680/month. Your 36% total-debt cap is $2,160/month, which leaves $1,660/month for housing once the $500 in existing debt is subtracted. Because $1,660 is lower than $1,680, your total-debt budget — not your housing budget — is the binding constraint, even though you're nowhere near maxing out the 28% test on its own.
How lenders actually apply this rule
Conventional lenders often anchor close to 28/36, but flex higher for borrowers with strong compensating factors: a high credit score, several months of cash reserves, or a long employment history. FHA guidelines commonly allow front-end/back-end ratios closer to 31/43, and VA loans focus more heavily on residual income than a strict ratio at all. Treat 28/36 as the conservative baseline, not the ceiling every lender enforces — see our FHA and VA affordability calculators for how those programs' own thresholds change the math.
Turning this into a home price
This calculator shows your recommended monthly housing budget. To translate that into an actual home price — factoring in your down payment, interest rate, taxes, and insurance — use the full Home Affordability Calculator. If you want to look at your ratios on their own first, the Debt-to-Income Calculator breaks down exactly which of your existing debts are eating into your budget.