The 28/36 rule is the gold standard for housing affordability: spend no more than 28% of gross monthly income on housing costs (mortgage principal, interest, taxes, and insurance), and no more than 36% on total debt payments (housing plus car loans, student loans, credit cards, and other obligations). On a household income of $100,000, this translates to a maximum monthly housing payment of $2,333. At a 6.5% mortgage rate with 20% down, this budget supports a purchase price of approximately $350,000 to $400,000 depending on local property tax rates and insurance costs.
However, this formula is just a starting point. The actual amount of house you can afford depends heavily on your specific financial situation and the local market. Property taxes vary dramatically across the country: New Jersey averages 2.49% annually while Hawaii averages just 0.28%. This single factor can swing your affordable price by $100,000 or more. Homeowner insurance similarly varies from $800 per year in some states to over $4,000 in hurricane-prone coastal areas.
Down payment requirements affect both what you can afford and your ongoing monthly costs. Conventional loans typically require 5-20% down, FHA loans require 3.5%, VA loans require 0%, and USDA rural loans require 0%. Putting less than 20% down triggers private mortgage insurance (PMI), which adds $50-200 per month until you reach 20% equity. This additional cost reduces the total purchase price your budget can support. For example, if PMI costs $150 per month, that effectively reduces your $2,333 budget to $2,183, which could mean a $20,000-$30,000 lower affordable price.
Interest rates are the largest variable in affordability calculations. The difference between a 5.5% and 7.5% rate on a $300,000 loan is nearly $400 per month, or $144,000 over the life of the loan. Rate shopping across multiple lenders and improving your credit score before applying can save tens of thousands of dollars. A credit score above 740 typically qualifies for the best available rates, while scores below 680 may see rates 1-2% higher.
Your debt-to-income ratio (DTI) matters as much as your income. Lenders calculate DTI by dividing your total monthly debt payments by your gross monthly income. Most conventional lenders require DTI below 43%, though some FHA programs allow up to 50%. If you carry $500 per month in car payments and $300 in student loans, that $800 reduces the mortgage payment you can qualify for by the same amount.
First-time buyer tip: get pre-approved before house hunting. Pre-approval tells you your actual approved amount based on your real credit, income, and debt, rather than a rough estimate. It also strengthens your offer in competitive markets because sellers know your financing is verified. The pre-approval process involves a credit check, income verification, and debt documentation, typically taking 1-3 days. Pre-approvals are usually valid for 60-90 days.