Buying a home is probably the largest financial decision you’ll ever make — and one of the most confusing, because the number a bank will lend you and the number you should borrow are almost never the same. “How much house can I afford?” sounds like a simple question, but the honest answer has a few moving parts: your income, your existing debts, the current interest rate, property taxes, insurance, and something called PMI if you put less than 20% down. This article walks you through all of it, step by step, using a rule of thumb that’s been a cornerstone of personal finance for decades. By the end, you’ll have a realistic number — not just a lender’s marketing pitch.
Why the Number Your Lender Gives You Is Usually Too High
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Here’s something the mortgage industry doesn’t advertise loudly: lenders are in the business of originating loans, which means their incentive is to tell you the maximum you qualify for, not the optimum for your financial life. A loan officer who tells you “congratulations, you’re approved for $650,000” is being accurate — but they’re not accounting for your retirement contributions, your kids’ daycare, the weekend trip you’d like to take once a year, or the fact that a water heater will fail on you in year three.
The Consumer Financial Protection Bureau explains in its guidance on debt-to-income ratios that lenders evaluate affordability primarily through your debt-to-income ratio (DTI) — the percentage of your gross (pre-tax) monthly income that goes toward debt payments. Many conventional lenders will approve borrowers with a DTI up to 43–50%. That’s a wide-open door. Walking through it doesn’t mean you should.
A more protective framework is the 28/36 rule, and it’s the one we’ll use as our foundation.
What the 28/36 Rule Actually Means
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The 28/36 rule sets two guardrails on your budget:
- The 28% front-end ratio: Your total monthly housing costs — principal and interest on the mortgage, property taxes, and homeowners insurance (sometimes bundled as “PITI”) — should not exceed 28% of your gross monthly income.
- The 36% back-end ratio: All of your monthly debt obligations combined — housing costs plus car payments, student loans, minimum credit card payments, and any other recurring debt — should not exceed 36% of gross monthly income.
Think of it this way: if you earn $6,000 a month before taxes, the 28% rule says keep housing at or below $1,680/month. The 36% rule says all your debts combined (including that $1,680) shouldn’t exceed $2,160/month.
By the numbers:
| Gross Monthly Income | 28% Housing Max | 36% Total Debt Max |
|---|---|---|
| $5,000 | $1,400 | $1,800 |
| $7,500 | $2,100 | $2,700 |
| $10,000 | $2,800 | $3,600 |
| $12,500 | $3,500 | $4,500 |
The gap between 28% and 36% is the space your non-housing debts can occupy. If you have no car loan, no student loans, no credit card debt — that gap is breathing room. If your existing debts are already eating into it, your comfortable housing budget shrinks accordingly.
Running the Calculator: A Real Example
Let’s put some real numbers on it. Imagine you and your partner earn a combined gross income of $9,000 per month ($108,000 per year). You have a $350/month car payment and $200/month in student loan minimums — $550 in existing monthly debt.
Step 1 — Find your housing ceiling: $9,000 × 0.28 = $2,520/month maximum for housing costs.
Step 2 — Check against the back-end rule: $9,000 × 0.36 = $3,240 total debt ceiling. Subtract your existing $550 in non-housing debt: $3,240 − $550 = $2,690 available for housing under the back-end rule.
The lower of the two numbers is your real ceiling. In this case, the front-end rule wins: $2,520/month for total housing costs.
Step 3 — Back into a purchase price: Your $2,520/month has to cover more than just the loan payment. Here’s a realistic breakdown on a $380,000 home with 10% down ($38,000). Using a 30-year fixed rate in the mid-6% range — consistent with Freddie Mac Primary Mortgage Market Survey averages reported in spring 2026 — the payment components look roughly like this:
- Principal & interest: ~$2,180
- Property tax estimate (1.1% annually ÷ 12): ~$348
- Homeowners insurance: ~$130
- PMI (explained below): ~$142
- Total: ~$2,800/month
That’s above the $2,520 ceiling. You’d need to either increase your down payment, look at homes priced lower, or reduce other debts first. This is exactly why running the math yourself — before touring homes — saves heartache.
Use the calculator embedded above to input your own income, debts, down payment, and local tax rate. It recalculates in real time and flags when you’ve crossed either the 28% or 36% threshold.
The PMI Factor: What It Is and When You Pay It
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If you put less than 20% down on a conventional loan, lenders require private mortgage insurance (PMI) — a monthly fee that protects the lender (not you) if you default. The CFPB’s explanation of private mortgage insurance describes it as coverage the lender takes out on your loan, with the cost passed on to you as the borrower.
PMI typically costs between 0.5% and 1.5% of your loan amount per year, divided into monthly payments. On a $342,000 loan (the amount borrowed after 10% down on a $380,000 home), 0.5% annual PMI would be $1,710/year or $142.50/month. The higher your loan-to-value ratio — the percentage of the home’s price you’re borrowing — the higher the PMI rate. The CFPB’s guidance on loan-to-value ratios explains how this ratio affects both your PMI cost and your overall loan terms.
The good news: PMI isn’t permanent. Under the federal Homeowners Protection Act, lenders must automatically cancel PMI once your loan balance reaches 78% of the original home value. You can also request cancellation at 80%. Ask your lender to document this milestone in writing at closing.
PMI matters for affordability calculations because it adds real monthly cost that disappears from the equation the moment you cross 20% equity — either by paying down the loan or through home appreciation. Many first-time buyers underestimate this line item and then feel pleasantly surprised when it drops off years later.
The Hidden Costs That Calculators Often Miss
The 28/36 rule is a solid foundation, but a full affordability picture also includes costs that don’t show up in a mortgage payment:
Maintenance and repairs. A common rule of thumb (sometimes called the 1% rule) suggests budgeting 1% of the home’s value per year for upkeep — about $3,800/year on a $380,000 home. Older homes and those with complex systems (pools, older roofs, aging HVAC) may run higher.
HOA fees. Homeowners association fees in condo or planned community settings range from under $100 to over $1,000 per month. These are recurring, often increase annually, and are not optional. They must be factored into your 28% ceiling.
Utilities. Moving from a 900-square-foot apartment to a 2,200-square-foot house means heating, cooling, and water bills will change meaningfully. Get estimates from the current owner before closing.
Closing costs. These are one-time at purchase — typically 2–5% of the loan amount — but they affect how much cash you have left for your down payment and emergency fund. Buyers who drain savings to reach a down payment target can end up in a financially fragile position, with little buffer for the maintenance and repair costs described above. The practical advice: after you find your 28/36 ceiling, subtract a mental buffer of $200–$400/month for variable ownership costs. That’s your real comfortable ceiling.
Rate Shopping: Don’t Leave Money on the Table
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Even a 0.25% difference in your mortgage interest rate changes your monthly payment meaningfully over a 30-year loan. On a $342,000 loan, the gap between 6.75% and 7.00% is roughly $58/month — that’s nearly $700/year and over $20,000 across the life of the loan.
When comparing lenders, look beyond the headline interest rate to the APR (annual percentage rate) — the all-in rate that includes lender fees and other costs. The CFPB’s consumer resources explain that APR is the more accurate figure for comparing loan offers on a like-for-like basis.
Some commonly used channels for comparing mortgage rates include large direct lenders, community banks, credit unions, and multi-lender marketplaces that let you see several quotes from a single application. Whichever path you choose, get quotes from at least three lenders and ask each one to quote the same loan type, term, and down payment so you’re comparing apples to apples.
A few ground rules: submit all your mortgage applications within the same 45-day window. Credit-scoring models treat multiple mortgage inquiries within that window as a single inquiry, protecting your credit score while you shop. Ask each lender to provide a Loan Estimate — the standardized three-page disclosure form that lenders are required to provide within three business days of receiving your application. The Loan Estimate makes side-by-side comparison straightforward because every lender uses the same format.
Your Realistic Next Step
The 28/36 rule isn’t the only framework for thinking about home affordability, but it’s the most durable one because it connects your housing costs to your whole financial picture — not just your ability to make one payment. Before you start touring homes, run your numbers in the calculator above, check both thresholds, and build in the buffer for ownership costs that won’t show up in any mortgage quote.
If the math works out, your next move is to get a pre-approval letter — a formal statement from a lender documenting how much they’ll lend you, based on verified income and credit. Pre-approval is different from pre-qualification (which is just an informal estimate); sellers take pre-approval seriously. Just remember: the letter will likely show a number higher than your 28/36 ceiling. That’s okay. You already know your real number.