Guide to home affordability
Reviewed 2025-06-24Why starting with income is smarter than starting with a listing price
Most first-time buyers approach the home search backwards. They browse Zillow or Redfin, fall in love with a $450,000 listing, then reverse-engineer whether they can afford it. By that point, emotional attachment makes objective financial analysis almost impossible. The smarter approach — the one financial advisors and mortgage professionals consistently recommend — is to determine your maximum home price before you look at a single listing.
Starting with your income anchors your search in financial reality. It means every home you visit is one you can actually afford, which eliminates wasted weekends and the disappointment of falling in love with a home that's out of reach. This calculator uses the same income-first methodology that lenders apply when they pre-qualify buyers.
The key insight: your maximum affordable home price is not determined by the home itself — it's determined entirely by your income, your existing debts, and your available down payment. Enter those three numbers accurately and this calculator gives you a number you can trust.
How the 28/36 rule works — and why lenders still use it in 2025
The 28/36 rule has been the backbone of US mortgage underwriting for decades, and it remains the primary qualification standard for conventional loans in 2025. It consists of two separate ratios that must both be satisfied.
The front-end ratio (28%) caps your total monthly housing cost — principal, interest, property taxes, homeowners insurance, and HOA fees — at 28% of your gross monthly income. If your household earns $10,000/month gross, your maximum housing payment is $2,800. This single number is the most important constraint in the calculation.
The back-end ratio (36%) caps your total monthly debt payments — housing plus car loans, student loans, minimum credit card payments, personal loans, and any other recurring obligations — at 36% of gross monthly income. Using the same $10,000/month example, your total debt ceiling is $3,600. If you already carry $700/month in car and student loan payments, only $2,900 is available for housing — and since $2,800 is lower, the front-end ratio binds.
Fannie Mae and Freddie Mac, who purchase the majority of conventional mortgages, use these thresholds because historical default data shows loans above these ratios fail at materially higher rates. FHA loans allow up to 43% back-end DTI with compensating factors; some VA loans go higher. But for standard conventional financing, 28/36 is what lenders use, and it's what this calculator applies.
The 28% number in practice
On a $120,000 household income, 28% of monthly gross ($2,800) supports roughly a $375,000 home at 7% over 30 years in a state with average property taxes. Raise the income to $150,000 and the same ratio supports approximately $470,000.
Debt-to-income ratio: what it means and why lenders scrutinize it
Debt-to-income ratio (DTI) is the single number lenders use to assess your ability to carry new debt. It's calculated by dividing your total monthly debt payments (including the proposed new mortgage) by your gross monthly income. A DTI of 33% means 33 cents of every pre-tax dollar you earn goes to servicing debt.
Lenders care about DTI because it directly measures financial cushion. A household with a 28% DTI has substantial income available for food, utilities, savings, and unexpected expenses after debt payments. A household at 43% DTI is using nearly half its gross income on debt obligations — a position that leaves little room for income disruption, medical expenses, or economic downturns.
The DTI indicator in the results above uses three thresholds: green (under 36%) means you're in the strongest approval tier for conventional loans; amber (36–43%) means approval is possible but lenders may require higher credit scores or larger cash reserves; red (above 43%) means most conventional programs are unavailable and you should focus on debt reduction before applying.
A practical point: lenders use gross income (before taxes) in DTI calculations, not take-home pay. Your actual cash flow is substantially lower. A borrower earning $120,000 gross in California takes home roughly $84,000 after taxes. Running DTI on gross income means the 28% rule is less conservative than it appears when evaluated against actual spending power.
Down payment, PMI, and the 20% threshold that changes everything
Your down payment percentage determines two critical outcomes: whether you pay Private Mortgage Insurance (PMI), and how much of your monthly payment builds equity versus paying interest.
PMI is required by virtually all conventional lenders when your down payment is below 20% of the purchase price. It is not optional — it is built into your loan as a condition of approval. PMI premiums typically range from 0.5% to 1.2% of the loan amount annually, added to your monthly payment. On a $400,000 loan, that's $2,000–$4,800 per year ($167–$400/month) in additional cost that builds no equity and provides no direct benefit to you as the borrower. It protects the lender against your potential default.
The 20% threshold eliminates PMI entirely, reduces your loan balance, and lowers your monthly payment across all components. It also signals to lenders that you have the financial discipline to accumulate significant savings, which correlates with lower default rates. Lenders reward this with the best available interest rates.
If your current savings put you below 20% down on your target price, you have three options: increase your down payment (save longer), target a lower home price (where your savings represent 20%+), or proceed below 20% and budget for PMI until you reach 20% equity through payments and appreciation.
PMI removal
Under the Homeowners Protection Act, you can request PMI cancellation when your loan balance reaches 80% of the original purchase price through payments. Lenders must automatically terminate it at 78%. However, this takes years — on a 30-year loan at 7%, you don't hit 80% LTV through payments alone until approximately year 8.
How state property taxes change affordability — dramatically
Property taxes are the most underestimated variable in home affordability calculations. Unlike mortgage interest rates — which vary by perhaps 1–2 percentage points across lenders — property tax rates vary by a factor of 6x or more across US states. This single variable can change your maximum affordable home price by $50,000–$100,000 on the same income.
Consider three states side by side on a $120,000 household income. In Hawaii (average effective rate: 0.32%), property tax on a $500,000 home is $133/month — barely affecting affordability. In California (0.76%), the same $500,000 home costs $317/month in taxes. In New Jersey (2.47%), the identical home costs $1,029/month in property taxes alone — nearly a third of the entire front-end housing budget for a $120,000 income earner.
The state selector in this calculator auto-populates the average effective property tax rate for the selected state, directly reducing the maximum home price your income can support. This reflects what you will actually pay as a new buyer assessed at current market value — not what a long-term owner with Proposition 13 protection might pay in California.
When relocating for work or lifestyle reasons, property tax rates should be part of the financial comparison. Moving from Illinois (2.23% average) to Florida (0.91%) on the same income and home price saves approximately $5,000–$7,000 per year in property taxes — a meaningful contribution to long-term wealth accumulation.
Running this calculator for maximum accuracy: a step-by-step guide
For the most accurate result, gather three documents before you run this calculator: your most recent pay stub (for gross annual income), your most recent credit card and loan statements (for monthly minimum payments), and your current savings balance (for down payment).
Enter your gross household income — this is before any taxes or deductions. If you have multiple income sources, include only stable, documented income that a lender can verify: W-2 wages, documented self-employment income, and consistent rental income. Do not include bonuses, overtime, or side income that you cannot document with 2 years of tax returns.
For monthly debts, include every recurring obligation that will appear on your credit report: car loans, student loans, minimum credit card payments, personal loans, child support, and alimony. Do not include utilities, groceries, subscriptions, or your current rent. Only debt obligations that show on your credit report count in DTI.
For down payment, enter the amount you have available after closing costs. Closing costs typically run 2–5% of the purchase price. On a $400,000 home, expect $8,000–$20,000 in closing costs above and beyond your down payment. If your savings are $80,000 total, your effective down payment after closing costs is roughly $60,000–$72,000.