The 28% and 36% Rules
These two ratios are the traditional starting point for home affordability. They've been used by lenders and financial planners for decades as a rough sanity check.
The 28% front-end rule says your total monthly housing payment — principal, interest, property taxes, and homeowner's insurance (PITI) — should not exceed 28% of your gross monthly income. If your household earns $7,000 per month before taxes, your maximum housing payment by this rule is $1,960.
The 36% back-end rule says your total monthly debt payments — housing plus car loans, student loans, credit cards, and any other debt — should not exceed 36% of gross income. That same $7,000 income household should have no more than $2,520 going to all debt combined.
Many lenders today have relaxed these guidelines. Conventional loans allow total DTI up to 43%, and FHA loans may allow up to 50%. But just because a lender will approve you at 43% DTI doesn't mean it's a comfortable place to be — a sudden job loss, medical bill, or rate adjustment can create serious strain at those ratios.
How Debt-to-Income Ratio Works
DTI is calculated by dividing your total monthly debt payments by your gross monthly income. If you earn $6,000/month and pay $500 in car payments, $300 in student loans, and are considering a $1,500 mortgage, your total monthly debt is $2,300. DTI = $2,300 ÷ $6,000 = 38.3%.
| DTI Range | Lender View | Reality |
|---|---|---|
| Below 36% | Excellent — best rates | Comfortable — meaningful buffer for emergencies |
| 36–43% | Acceptable for most loans | Tight — little room for unexpected expenses |
| 43–50% | FHA may approve; conventional unlikely | Stressful — most of income committed to debt |
| Above 50% | Most lenders decline | Unsustainable for most households |
Source: CFPB mortgage guidelines. Actual lender requirements vary.
Run the Real Calculation
Here's a more useful approach than the gross income ratios. Use your actual take-home pay, not your gross salary.
Step 1 — Find your monthly take-home pay. After taxes, 401(k) contributions, and health insurance, what actually deposits in your bank? This is your true available income.
Step 2 — List existing monthly debt payments. Car, student loans, minimum credit card payments. Add them up.
Step 3 — Budget essential non-debt expenses. Food, utilities, insurance, childcare, transport, subscriptions. Be honest.
Step 4 — See what remains. Take-home pay minus debts minus essentials = your maximum comfortable housing budget. A mortgage payment above that number creates financial stress, regardless of what the lender approves.
According to the CFPB's 2024 consumer credit data, homeowners who took on mortgages above 38% DTI were significantly more likely to report financial stress and miss payments during periods of income disruption than those who stayed below 35%. Source: consumerfinance.gov.
Hidden Costs of Homeownership
One of the most common mistakes first-time buyers make is budgeting only for the mortgage payment. The full monthly cost of owning a home includes several additional expenses that can add $500–$1,500 per month depending on the home and location.
- Property taxes. These vary enormously by location — from under 0.5% to over 2.5% of home value annually. On a $400,000 home in a high-tax area, that's $10,000 per year or $833/month.
- Homeowner's insurance. Typically $1,200–$3,000 per year ($100–$250/month) depending on location, home value, and coverage.
- Private mortgage insurance (PMI). Required if your down payment is below 20%. Typically 0.5–1.5% of the loan amount annually — on a $350,000 loan, that's $1,750–$5,250 per year or $146–$438/month.
- HOA fees. If applicable — can range from $100 to $1,000+ per month for condos or gated communities.
- Maintenance and repairs. Budget 1% of the home's value per year. A $400,000 home requires a $4,000/year ($333/month) budget for repairs, appliances, and upkeep. Older homes may need more.
How Your Down Payment Changes the Math
The same home can have very different monthly costs depending on how much you put down. A larger down payment means a smaller loan, lower monthly payment, and no PMI once you hit 20%.
| Home Price | Down Payment | Loan Amount | Est. Monthly Payment (6.8%) | PMI |
|---|---|---|---|---|
| $400,000 | 3% ($12,000) | $388,000 | ~$2,540 | Yes (~$250/mo) |
| $400,000 | 10% ($40,000) | $360,000 | ~$2,355 | Yes (~$180/mo) |
| $400,000 | 20% ($80,000) | $320,000 | ~$2,093 | No PMI |
Estimates based on 30-year fixed rate of 6.8%. Excludes taxes and insurance. Actual payments vary by lender.
Home Affordability in the UK, India, and Canada
UK: UK lenders use a similar DTI concept but also stress-test your mortgage — checking whether you could still afford payments if rates rose by 3%. Most UK lenders cap mortgages at 4–4.5x annual income (though some go higher with larger deposits). The average UK house price is around £290,000, making affordability a significant challenge in London and the South East. The MoneyHelper affordability guide is available at moneyhelper.org.uk.
India: Indian banks typically offer home loans up to 80–90% of the property value. EMI (monthly instalment) should generally not exceed 40–50% of net monthly income per lender guidelines set by the RBI. Interest rates on home loans range from 8.5–10% at major banks. The National Housing Bank (NHB) regulates housing finance at nhb.org.in. First-time buyers may qualify for benefits under the Pradhan Mantri Awas Yojana (PMAY) scheme.
Canada: The Canadian mortgage stress test requires buyers to qualify at a rate 2% higher than their actual rate or 5.25%, whichever is higher. Maximum GDS (Gross Debt Service) ratio is 39%, and maximum TDS (Total Debt Service) is 44%. CMHC mortgage insurance is mandatory if your down payment is below 20%. Details at cmhc-schl.gc.ca.