Last updated: March 2026
What Is a Mortgage Affordability Calculator?
A mortgage affordability calculator answers the most important question in home buying: How much house can I actually afford? With over 1 million monthly searches for "how much house can I afford," it is the single most common financial question people ask when starting the home-buying process.
Unlike a standard mortgage calculator that starts with a home price, this tool works backwards from your finances — your income, existing debts, down payment, and credit profile — to determine the maximum home price you can comfortably support. It uses the same 28/36 DTI (debt-to-income) rule that mortgage lenders apply when evaluating your application.
How to Calculate Mortgage Affordability
The calculation follows a specific process that mirrors what lenders do when evaluating your loan application:
Step 1: Calculate your maximum housing payment. Multiply your gross monthly income by 0.28 (the front-end ratio). If you earn $75,000/year, your gross monthly income is $6,250, and 28% of that is $1,750 — your maximum total housing cost.
Step 2: Apply the back-end ratio. Multiply gross monthly income by 0.36, then subtract existing monthly debts. With $500/month in debts: $6,250 x 0.36 = $2,250 - $500 = $1,750. Your effective maximum is the lower of the front-end and back-end results.
Step 3: Subtract non-P&I costs. From your maximum housing payment, subtract property taxes, homeowner's insurance, PMI (if applicable), and HOA fees. The remainder is what you can spend on principal and interest.
Step 4: Reverse the amortization formula. Using your available P&I budget, interest rate, and loan term, the calculator works backwards to find the maximum loan amount. Add your down payment to get the maximum home price.
The median U.S. home price reached $396,900 in 2025 according to the National Association of Realtors. At today's rates, a household needs roughly $85,000-$100,000 in income to afford the median home with 20% down — highlighting why affordability analysis matters more than ever.
The 28/36 Rule Explained
The 28/36 rule sets two guardrails on how much of your income should go toward debt. The front-end ratio (28%) caps your housing expenses, while the back-end ratio (36%) caps all debt combined. These are not hard limits — FHA loans may approve up to 50% DTI, and VA loans have no fixed cap — but they represent what most financial planners consider safe.
A common mistake is ignoring existing debts when calculating affordability. Someone with $1,500/month in car and student loan payments will qualify for significantly less home than someone with the same income and no debts. Paying down high-interest debt before buying often increases your purchasing power more than saving a larger down payment.
Frequently Asked Questions
How much house can I afford on a $75,000 salary?
Using the 28% front-end DTI rule, your max monthly housing payment is $1,750 ($75,000 / 12 x 0.28). At 6.5% for 30 years with 20% down, that supports a home around $290,000-$310,000 depending on local property taxes and insurance costs. With $500/month in existing debts, the 36% back-end rule may further limit your budget.
What is the 28/36 rule for mortgage affordability?
The 28/36 rule is the standard guideline lenders use. The front-end ratio (28%) means your total housing payment — principal, interest, taxes, insurance, PMI, and HOA — should not exceed 28% of your gross monthly income. The back-end ratio (36%) means all debt payments combined (housing + car + student loans + credit cards) should stay under 36% of gross income. Your effective limit is the lower of the two.
How does my credit score affect what I can afford?
Credit score directly impacts your interest rate. Excellent credit (740+) can get rates 0.25-0.5% below average, while poor credit (below 580) may add 1-1.5% to your rate. On a $250,000 loan, each 0.5% rate increase reduces your buying power by roughly $15,000-$20,000. Improving your score before buying can save tens of thousands over the life of the loan.
Should I buy the most expensive home I can afford?
Financial advisors generally recommend buying below your maximum. The 28% DTI ceiling is what lenders will approve, but the 25% 'comfortable' level leaves room for savings, emergencies, home repairs, and lifestyle expenses. First-time buyers often underestimate maintenance costs (typically 1-2% of home value annually) and the difference between pre-approval amounts and true affordability.
How does PMI affect my affordability?
Private Mortgage Insurance (PMI) is required when your down payment is less than 20%, typically costing 0.35-1.0% of the loan annually. On a $250,000 loan, that adds $73-$208/month to your payment. This reduces the amount available for principal and interest, lowering the home price you can afford by $10,000-$30,000. PMI automatically drops when you reach 20% equity.