How much house can you actually afford?

Buying a home is the largest financial decision most people will ever make. Yet study after study shows that buyers consistently overestimate how much house they can afford, focusing on the listing price rather than the monthly carrying cost. The Affivance Home Affordability Calculator removes the guesswork by applying the same debt-to-income (DTI) ratios and mortgage formulas used by Fannie Mae, Freddie Mac, and major lenders across the United States, Canada, the United Kingdom, and Australia.

The 28/36 rule explained

Lenders use two related ratios to gauge whether a borrower can comfortably repay a mortgage. The front-end ratio (also called the housing ratio) caps your total monthly housing payment — principal, interest, property taxes, homeowner’s insurance, and HOA dues (collectively PITI) — at 28% of your gross monthly income. The back-end ratio (total debt ratio) caps your total monthly debt obligations — including the housing payment plus credit cards, auto loans, student loans, child support, and any other recurring debt — at 36% of gross monthly income.

Together these form the “28/36 rule,” the foundation of conservative mortgage underwriting since the 1970s. Some loan programs allow higher limits: FHA loans permit a 31/43 ratio, VA loans use residual income tests, and conventional loans backed by Fannie Mae can go to 45% DTI in certain cases. The Affivance calculator lets you adjust these ratios to model more aggressive scenarios (30/36, 33/40, 33/43) so you can see exactly how stretching the ratios changes your maximum purchase price.

How the calculator works

The calculator works backward from your monthly budget to a maximum home price. First it computes gross monthly income by dividing annual income by 12. It then multiplies that figure by the housing ratio to find the maximum PITI payment, and by the debt ratio to find the maximum total debt payment. Subtracting your existing monthly debt from the maximum total debt yields the amount available for housing under the back-end test. The smaller of the two caps — front-end or back-end — becomes your binding PITI limit.

From that PITI limit the calculator subtracts monthly property taxes, homeowner’s insurance, and HOA dues to isolate the amount available for principal and interest. It then inverts the standard amortization formula to solve for the maximum loan amount:

P = M × [(1+r)ⁿ − 1] ÷ [r × (1+r)ⁿ]

where:
  P = loan amount (principal)
  M = monthly principal & interest payment
  r = monthly interest rate (annual rate ÷ 12 ÷ 100)
  n = total number of monthly payments (years × 12)

Adding your down payment to that loan amount produces the maximum affordable home price. This is the exact methodology used by Bankrate, NerdWallet, and Calculator.net, which is why our results match those tools to within a penny.

What counts as monthly debt?

The back-end ratio includes any obligation that appears on your credit report with a fixed monthly payment: minimum credit card payments (typically 1-3% of the balance), auto loans and leases, student loans (even in deferment, most lenders count 1% of the balance), personal loans, child support and alimony, co-signed loans, and timeshare payments. Utilities, cell phone bills, subscriptions, and groceries are not counted because they are discretionary or variable. If you pay off a credit card in full each month, the lender still uses the minimum payment shown on your credit report.

Factors that quietly reduce your budget

Many first-time buyers are surprised that their actual maximum purchase price falls short of what online calculators estimated. The culprits are usually property taxes, insurance, HOA dues, and private mortgage insurance. Property taxes vary dramatically by location — the U.S. national average is about 1.1% of home value per year, but in parts of Texas, Illinois, and New Jersey, effective rates exceed 2.3%. On a $400,000 home, that’s the difference between $367/month and $767/month — a swing that can reduce your loan amount by more than $60,000.

Homeowner’s insurance has risen 20-40% since 2022 in many states due to climate-related losses. Budget $1,500-$3,500 annually depending on location and coverage. HOA dues can range from $30 for basic services to $800+ for full-amenity condos. Lenders include these in your housing ratio, so a $400 HOA payment reduces your maximum loan by roughly $60,000 at current rates. Private mortgage insurance (PMI) applies when your down payment is less than 20%; expect 0.3-1.5% of the loan amount annually, paid monthly. This calculator does not include PMI — add it manually if your down payment is under 20%.

Interest rates remain the single biggest lever. A 1% rate increase reduces purchasing power by roughly 10-12%. Shopping three or more lenders can easily save 0.25-0.5% on your rate, which translates to tens of thousands of dollars in additional borrowing capacity.

How to improve your affordability

If the calculator shows you’re a few thousand dollars short of your target price, you have four realistic levers. First, increase your down payment — every additional $1,000 down is $1,000 less you need to borrow, and the savings compound because you pay interest on a smaller balance. Second, pay down existing debt — reducing your monthly debt payments by $200 increases your maximum housing payment by $200, which can translate to $30,000-$40,000 more borrowing power at current rates. Third, lock a lower rate — a 0.5% rate reduction can add $15,000-$25,000 to your max purchase price. Fourth, lengthen the term — moving from a 15-year to a 30-year mortgage dramatically lowers your monthly payment and increases max loan amount, but you’ll pay far more interest over the life of the loan.

The hidden costs of homeownership

Affordability is more than the mortgage payment. Plan for maintenance (1-2% of home value annually), closing costs (2-5% of purchase price), moving and furnishing ($5,000-$15,000), and property tax reassessment after purchase (especially in California under Prop 13). A house you can “afford” by the 28/36 rule may still feel tight if you ignore these. Conservative buyers target a 25/30 ratio to leave breathing room.

DTI and affordability status

Your debt-to-income ratio is the single most important number in the mortgage process. The Affivance calculator classifies your DTI into four tiers. Excellent (≤36%): you qualify for the best rates and most loan programs. Acceptable (36-43%): you’ll qualify for most conventional and FHA loans, but with tighter scrutiny. High Risk (43-50%): only non-QM lenders and portfolio loans will likely approve you, and rates will be 1-2% higher. Not Affordable (>50%): you will almost certainly be denied — reduce debt or increase income before applying.

Country-specific notes

The calculator adapts its currency formatting and date conventions for the United States (USD, MM/DD/YYYY), Canada (CAD, DD/MM/YYYY), the United Kingdom (GBP, DD/MM/YYYY), and Australia (AUD, DD/MM/YYYY). Underwriting conventions vary slightly: Canada uses the Gross Debt Service (GDS) ratio of 32% and Total Debt Service (TDS) of 40% under CMHC rules; the UK typically caps lending at 4.5× income under FCA stress-test guidelines; Australia’s APRA requires lenders to assess serviceability at a 3% buffer above the actual rate. The 28/36 framework used here is a reasonable cross-border approximation, but always confirm with a local lender.