How this instrument works
28/36 is a pair of debt-to-income ceilings conventional mortgage underwriters lean on when sizing up how large a loan borrowers can carry. Front-end caps housing cost — principal, interest, property tax and insurance — at 28% of gross monthly income. Back-end caps every recurring debt payment combined, housing included, at 36%. Both come from one income figure at once, which is why this instrument returns two answers from one entry.
Two ceilings answer different questions. Front-end tests whether housing itself fits a paycheck; back-end tests whether that house fits alongside car payments, student loans, and minimum credit-card payments already on the books. A borrower can pass one test and fail the other — someone with no other debt might qualify for housing well past 28% under back-end math lenders use, while someone carrying heavy installment debt can find housing room squeezed below 28% even though income alone looks generous.
Both figures are screening thresholds, not entitlements or requirements. Lenders vary exact ceilings by loan program — FHA and VA underwriting routinely tolerates back-end ratios near 41–43% given strong credit or cash reserves — and this 28/36 split says nothing about property tax rates, insurance premiums, or how comfortable any household actually feels at that payment. Treat these two numbers as first filters, not a budget.
- Enter your pre-tax monthly earnings in Gross monthly income, $ — this is pay before deductions, not take-home pay.
- Read Housing limit (28%) — roughly what a lender applying front-end guidelines would count toward principal, interest, tax and insurance.
- Read Total debt limit (36%) — a ceiling on that housing payment plus every other recurring debt combined.
- Compare that gap between both limits against your actual non-housing debt to see how much room a back-end ratio really leaves.
Worked example — a $6,000 monthly income
A borrower earning $6,000 gross monthly runs both formulas at once. Housing limit: $6,000 times 0.28 equals $1,680 — roughly what a lender's front-end test would allow toward principal, interest, tax and insurance combined. Total debt limit: $6,000 times 0.36 equals $2,160 — a ceiling on that housing payment plus every other recurring obligation.
That $480 gap between two figures leaves room for everything not housing: a car payment, student loan installment, minimum card payments. If this borrower already carries $500 a month in other debt, realistic housing ceiling drops to $1,660 under back-end math — just under that $1,680 front-end figure — showing why lenders check both ratios rather than either alone.
Questions
What counts as debt in the 36% total debt limit?
Recurring, reported obligations: a projected housing payment, minimum credit-card payments, auto loans, student loans, personal loans and alimony or child support you owe. It excludes day-to-day spending like groceries, utilities, subscriptions, and insurance other than homeowner's, and lenders typically drop any debt with fewer than about ten payments left.
Why do the two ceilings sometimes point in different directions?
Because they test different things from one income figure. That 28% figure only checks whether a housing payment alone fits a paycheck; that 36% figure checks housing plus every other debt together. A borrower with no car or student loan can clear 28% comfortably while someone with heavy installment debt hits that 36% ceiling first, well below what housing alone would allow.
Is 28/36 a hard rule lenders always enforce?
No — it is a conventional-loan guideline, and actual limits shift by program. FHA loans commonly tolerate back-end ratios near 41–43%, VA loans weigh residual income more than a fixed ceiling, and strong credit scores or large cash reserves can push either number higher at a lender's discretion. Treat 28/36 as a starting estimate, not the figure your specific lender will quote.
Does gross income mean pay before or after tax?
Before. Both ratios use gross monthly income — pay before income tax, payroll tax and other deductions — because that is a figure lenders pull from pay stubs and tax returns to standardize comparisons across borrowers. Using take-home pay instead will overstate how much room 28% and 36% ceilings actually leave.
How is this different from a budgeting rule like 50/30/20?
50/30/20 is a personal budgeting habit covering needs, wants and savings across an entire paycheck. 28/36 is narrower and specific to mortgage qualification — it only addresses housing and debt, says nothing about savings or discretionary spending, and exists because lenders, not household budgets, use it to decide how large a loan to approve.
Why did my lender's DTI figure come out different from this calculator?
Lenders often adjust that formula with overlays: they may include projected property tax and insurance on a home you have not chosen yet, exclude debts close to payoff, or count only a percentage of rental income. This instrument applies a textbook 28% and 36% split cleanly against income you enter — your lender's underwriting software layers its own program-specific rules on top.
References
- CFPB — How lenders evaluate loan options and qualify borrowers
- Federal Reserve — Consumer's guide to mortgage settlement costs
Read this first: This instrument shows arithmetic, not advice. Real offers add fees, taxes and terms that vary by lender and place — verify the figures against your actual paperwork before deciding anything.