Home Affordability Calculator

Estimate how much home you can afford based on income, debt, and down payment.

Status: Algorithmic Audit (CPA Review Pending)
Jurisdiction: United States (IRS & SSA Standards)
Tax Year / Constants: 2026 Statutory Limits
Data Privacy: 100% Client-Side In-Browser

The Mathematical Formula

Max Allowable Monthly Housing (PITI) = min(Gross Monthly Income × 28%, Gross Monthly Income × 36%-43% - Existing Monthly Debt)

Variable & Parameter Definitions

  • Front-End DTI (28%) Maximum allowable percentage of gross income allocated to housing costs (Principal, Interest, Property Taxes, Insurance, HOA).
  • Back-End DTI (36%-43%) Maximum allowable percentage of gross income allocated to ALL debts (Housing + Auto Loans + Student Loans + Credit Cards).
  • Existing Monthly Debt Total recurring minimum monthly debt obligations reported on your credit bureau reports.
  • Max Purchase Price Affordable home price derived from allowable monthly PITI, prevailing interest rate, and available down payment.

Real-World Worked Scenario: Household Earning $120,000/Year with $600 Monthly Debt

A buyer earning $10,000 gross monthly ($120k/yr) with $600 in car and student loan payments evaluates max affordable home price at 6.5% interest with $60,000 down.

  1. Front-End Limit (28% Rule): $10,000 × 0.28 = $2,800 maximum monthly housing budget.
  2. Back-End Limit (36% Rule): ($10,000 × 0.36) - $600 existing debt = $3,600 - $600 = $3,000 monthly.
  3. Governing Constraint: The lower figure of $2,800/month governs maximum allowable PITI.
  4. PITI Breakdown: Taxes, insurance, and HOA reserve (~$650/mo), leaving $2,150 available for Principal & Interest.
  5. Max Borrowing Capacity: $2,150 monthly payment at 6.5% for 30 years supports a $340,000 loan.
  6. Max Home Purchase Price: $340,000 loan + $60,000 down payment = $400,000 maximum affordable home.
Key Financial Takeaway: Lenders approve homes based on gross income before taxes, but wise buyers budget based on net take-home pay to avoid becoming "house-poor."

Strategic Insights & Pitfalls to Avoid

  • ✓ The 3x Income Guideline: A common traditional benchmark is purchasing a home priced at roughly 3.0x to 3.5x annual gross household income.
  • ✓ Property Tax Variations: In high-tax states (New Jersey, Texas, Illinois), property taxes can consume 30% to 40% of your total monthly housing payment.
  • ✓ Emergency Fund Protection: Never drain all liquid cash for your down payment; retain 3 to 6 months of expenses for unexpected home repair emergencies.

Frequently Asked Questions

What is the 28/36 rule in mortgage qualification?

A standard mortgage qualification rule: no more than 28% of gross monthly income should go toward housing, and no more than 36% toward all total debt payments combined.

Can I qualify for a mortgage with a DTI above 43%?

Yes. Certain automated underwriting systems approve conventional loans up to 45%–50% DTI, and FHA loans can extend up to 50% DTI with compensating factors.

How does paying off a car loan affect home affordability?

Eliminating a $500/month auto payment frees up $500/month in back-end DTI, boosting your mortgage borrowing power by roughly $75,000 to $80,000.

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