The honest answer to “how much house can I afford?” is two different numbers: what feels affordable to you, and what a lender will approve. They’re rarely the same. This guide shows you how lenders arrive at their number — so you can work backward to yours before you start touring homes.
What “Afford” Means to a Lender
A lender doesn’t care how much you want to spend or what your budget feels like. They have one question: given your income and your existing debts, is this housing payment likely to get paid every month?
They answer that question with two ratios:
- PITI — the total monthly housing payment
- DTI — your total monthly debt obligations as a percentage of gross income
If your PITI is too high relative to your income, or your total debts push your DTI past their threshold, the loan doesn’t close. It doesn’t matter that the payment “feels fine” or that you’ve been paying $2,400 a month in rent without missing a beat.
The PITI Formula, Explained Simply
PITI stands for Principal, Interest, Taxes, and Insurance. It’s the real monthly cost of owning a home — not just the payment on the loan itself.
Principal and Interest (P&I)
This is the part most calculators show. On a $380,000 loan at a 7% fixed rate, the monthly P&I payment is roughly $2,529. This number doesn’t change over the life of the loan (for a fixed-rate mortgage), but it’s only part of what you’ll pay.
Property Taxes
Property taxes are collected monthly as part of your mortgage payment and held in an escrow account. They vary significantly by location — from under 0.5% of assessed value annually in some states to over 2% in others. On a $450,000 home in a state with a 1.1% effective rate, that’s roughly $412 per month added to your payment.
Homeowner’s Insurance
Lenders require this. A rough rule of thumb is $100–$150 per month for a mid-priced home, though it varies by location, home age, and coverage level.
PMI and HOA
If your down payment is less than 20% on a conventional loan, you’ll also pay private mortgage insurance (PMI) — typically 0.5%–1.5% of the loan amount per year, divided monthly. On a $380,000 loan, PMI at 0.8% adds about $253/month.
HOA dues, if applicable, are included in the back-end DTI calculation even if they’re paid separately from the mortgage.
Full PITI example:
| Component | Monthly Cost |
|---|---|
| Principal & Interest (7%, $380k loan) | $2,529 |
| Property taxes (1.1% rate, $450k home) | $412 |
| Homeowner’s insurance | $125 |
| PMI (0.8% on $380k) | $253 |
| Total PITI | $3,319 |
This is what a lender calls your housing payment. Not $2,529.
How DTI Caps Your Maximum Purchase Price
Your debt-to-income ratio is the constraint that limits how much house you can buy, regardless of what you think you can handle.
Front-End DTI (Housing Ratio)
This is just your PITI divided by your gross monthly income. Most conventional loan programs want this below 28%–31%.
Example: $3,319 PITI ÷ $10,000 gross monthly income = 33.2% front-end DTI — above the preferred threshold.
Back-End DTI (Total Debt Ratio)
This is your PITI plus all other monthly debt obligations (car payments, student loans, minimum credit card payments, personal loans) divided by gross income.
Most conventional loans allow back-end DTI up to 45%–50%. FHA programs are somewhat more flexible. Underwriters focus most heavily on this number.
Example: $3,319 PITI + $600 in other monthly debts = $3,919 total ÷ $10,000 income = 39.2% back-end DTI — within conventional guidelines.
A Worked Example
Buyer profile:
- Gross annual income: $110,000 ($9,167/month)
- Monthly debts: $550 (car payment + student loan minimums)
- Down payment: $50,000
- Property tax rate: 1.2%
Step 1: Find the maximum monthly PITI using back-end DTI
If the lender’s max back-end DTI is 45%: $9,167 × 0.45 = $4,125 maximum total debt payment. Subtract existing debts: $4,125 − $550 = $3,575 available for PITI.
Step 2: Back out of PITI to find loan amount
Assume taxes/insurance/PMI total ~$750/month (reasonable for a home in this price range). That leaves $3,575 − $750 = $2,825 for P&I.
At 7%, $2,825/month in P&I supports roughly a $425,000 loan.
Step 3: Add down payment for purchase price
$425,000 loan + $50,000 down = approximately $475,000 maximum purchase price.
This isn’t a guarantee — the lender will verify everything — but it gives you a working ceiling before you start touring homes.
What This Means for Your House Search
Two buyers with the same income can qualify for very different purchase prices based on their existing debts. A buyer with $1,200/month in car and student loan payments will qualify for tens of thousands less than a buyer who has paid off those obligations.
Before you talk to a lender, know your numbers:
- Your gross monthly income (before taxes, all sources you can document)
- Your monthly debt obligations that appear on your credit report
- Your available down payment and closing cost reserves
The Affordability Calculator on LendingPulse runs the full PITI and DTI calculation together — plug in your income, debts, down payment, local tax rate, and insurance estimate to get a realistic purchase price ceiling. It also shows you how each variable (more income, less debt, larger down payment) moves the number, which is more useful than any single answer.
If you want to understand how each line of that output is calculated, Mortgage Calculator 101 walks through every number a calculator produces and what it actually represents.