28/36 Rule Calculator

Understanding the 28/36 Debt Rule

The 28/36 rule emerged from decades of mortgage underwriting practice and remains the industry standard for evaluating borrower risk. Banks and credit unions rely on it because borrowers whose housing expenses stay under 28% of income statistically demonstrate lower default rates.

The rule divides into two components:

• Front-end ratio (28%): Housing costs divided by gross monthly income. Housing costs typically include principal, interest, property taxes, and homeowners insurance—commonly abbreviated as PITI.
• Back-end ratio (36%): All monthly debt payments (housing plus car loans, credit cards, student loans, etc.) divided by gross monthly income.

Most lenders will approve a mortgage only if both ratios fall within these thresholds, though some will stretch to 40% on the back-end ratio for borrowers with excellent credit histories or substantial down payments.

28/36 Rule Calculations

The calculator computes two key ratios by dividing your debt obligations by your gross monthly income:

• Income — Your gross monthly income before taxes and deductions
• Housing costs — Sum of monthly principal, interest, property taxes, and insurance (PITI)
• Other debts — Monthly payments on auto loans, credit cards, student loans, and other obligations

Practical Example: Does Your Budget Fit the Rule?

Suppose your gross monthly income is $5,000. Your mortgage payment (including taxes and insurance) totals $1,100 per month, and you carry $400 in car loan and credit card payments.

Front-end ratio: $1,100 ÷ $5,000 = 22%. This clears the 28% threshold comfortably.

Back-end ratio: ($1,100 + $400) ÷ $5,000 = 30%. You're within the 36% limit with headroom for unexpected expenses.

In this scenario, a lender would likely approve additional borrowing, and you're demonstrating responsible debt management. However, if your total debt reached $1,900 per month, your back-end ratio would hit 38%—triggering a decline from most traditional lenders.

Key Caveats When Using the 28/36 Rule

The rule provides a useful benchmark, but several real-world factors can shift its applicability:

1. Gross income, not take-home pay — The 28/36 rule uses gross income, not what you actually deposit each month. A $5,000 gross salary might net only $3,500 after taxes and benefits. Calculate your true spending capacity against net income, not the lending standard.
2. The rule ignores your lifestyle expenses — Passing the 28/36 test means lenders think you can afford it—not that you can comfortably live on what remains. Budget for groceries, utilities, insurance, childcare, and savings before committing to maximum housing costs.
3. Interest rates and property taxes vary by region — Borrowing costs differ dramatically across markets and change with economic conditions. A house affordable at 3% mortgage rates becomes unaffordable at 7%. Factor in local property tax rates, which can swing payments by hundreds of dollars monthly.
4. Future debt obligations matter — The rule evaluates your current debt load, but not upcoming major expenses. If you're planning children, job transitions, or vehicle replacement, your true back-end ratio may be much higher than today's snapshot suggests.

When and How Lenders Apply the 28/36 Rule

Most conventional lenders enforce the 28/36 rule as a hard ceiling for mortgage qualification, though flexibility exists:

• FHA loans may permit up to 43% back-end ratios for borrowers with strong credit and substantial equity reserves.
• VA and USDA loans sometimes approve ratios exceeding 41% given the loan guarantees backing them.
• Portfolio lenders (banks holding mortgages rather than selling them) occasionally negotiate above-guideline ratios for longtime customers or unique situations.

The rule assumes you want a 30-year amortizing loan; shorter loan terms or interest-only periods alter the calculation's practical relevance. It also assumes stable income—self-employed borrowers or those with variable compensation face additional scrutiny beyond the ratio test.