"How much house can I afford?" is the most-Googled mortgage question — and the most misunderstood. People expect a vibe: a salary multiple, a gut feeling, a number a friend mentioned. Lenders don't work on vibes. Your approval is driven by one cold, mechanical thing: debt-to-income ratio. Once you understand DTI, the honest number stops being a mystery — and you can decide for yourself how much of it you actually want to use.
Approval is math, not vibes
A lender's job is to answer one question: can this borrower comfortably make this payment every month given everything else they owe? To answer it, they don't look at your dreams — they look at your income and your monthly debts. The new house payment gets added to your existing obligations, and the whole pile is compared to your gross monthly income. That ratio is the approval.
The four inputs that set your number
Every honest affordability estimate runs on the same four ingredients. Change any one and the number moves:
| Input | What it does |
|---|---|
| Gross monthly income | The denominator of every ratio — bigger income, bigger room. |
| Monthly debts | Car loans, student loans, minimum card payments — these eat into your room before the house even counts. |
| Down payment | More down = smaller loan, lower payment, and you may dodge or shrink mortgage insurance. |
| Interest rate | The payment lever. A higher rate shrinks how much house the same payment buys. |
The 28/36 guideline, explained
The oldest rule of thumb in mortgage lending is 28/36, and it's really two ratios:
- 28% front-end: your total housing payment — principal, interest, taxes, insurance, and any HOA — ideally stays around 28% of your gross monthly income.
- 36% back-end: your housing payment plus all other debt ideally stays around 36% of gross income.
It's a guideline, not a law — but it's where the conversation starts, and it's a good sanity check on comfort.
Your gross income is the plate. Your existing debts are food already on it — the car payment, the student loan, the credit cards. The lender will only let the mortgage take up so much of what's left. If your plate is already half full of other debt, there's less room for house, no matter how big your appetite. Clear some debt off the plate and suddenly there's room for a bigger main course.
Approved-for vs. comfortable-with: don't confuse them
Here's the trap that catches good earners. The lender hands you a maximum — say, the biggest payment that fits at 43% back-end — and it feels like a target. It isn't. It's a ceiling, not a recommendation. Approval math doesn't know about your daycare costs, your travel, your retirement savings, or the water heater that's going to fail in year three.
Plenty of financially sharp buyers deliberately shop below their approval so the payment leaves breathing room. Being "house poor" — approved for a number that leaves nothing left over — is a real and avoidable mistake.
Want a bigger number? Pull the right levers
Because it's all DTI, you can move your approval on purpose:
- Lower your monthly debts. Paying off a car loan can free up more buying power than a raise.
- Document more income. Bonuses, overtime, and side income can count if it's stable and provable.
- Put more down. A smaller loan means a smaller payment and a friendlier ratio.
- Improve your credit. Better scores unlock better pricing, which lowers the payment at the same loan size.
Get the honest number first
Before you fall in love with a listing, run your four inputs through a real affordability calculator — income, monthly debts, down payment, and a realistic rate. It'll show you both the ceiling and a comfortable target, so you walk into the market knowing your number instead of guessing.
Questions to ask before you shop
- "What's my back-end DTI at the payment I'm considering?"
- "What's the max I'm approved for vs. the payment I'd actually be comfortable with?"
- "Which of my monthly debts, if paid off, would move my approval the most?"
- "Does this estimate include taxes, insurance, and HOA — not just principal and interest?"
Want your honest number in two minutes?
Run the free affordability calculator on the homepage, then grab the Stuck Homeowner's Playbook to see the comfortable target — not just the ceiling.
Get the Free Playbook →Frequently asked questions
Related free tools: Affordability calculator · Mortgage Payment + MI calculator · Credit guides
Educational content only — not financial, mortgage, or legal advice, and not a loan offer or solicitation. Timothy George is the founder of Infinity Financial Mortgage Corporation and a former mortgage professional with 20+ years in mortgage and auto finance; he is not currently licensed, and this is independent educational material. DTI limits, guidelines, and program rules vary by lender and change over time — confirm specifics with a currently-licensed professional before you act.