Mortgage 101: How much house can you actually afford? (What lenders really look at)
I had a really great loan application with 1st time homeowners yesterday, and it made me realize that there is a lot of misinformation on this topic. I tried to condense this, but there is a lot to unpack...
The 28/36 "rule" is a budgeting guideline, not what lenders use
You've probably heard "keep housing under 28% of income, total debt under 36%." That's fine personal finance advice. But it's not how lenders approve loans.
What lenders actually look at is your debt-to-income ratio (DTI) and the limits are way higher than most people realize.
Real DTI limits by loan type
Conventional loans : back-end up to 50% DTI
FHA loans: front-end is a hard cap at 47%, no exceptions. Back-end can stretch to 55–57% with compensating factors. These are separate limits — both apply.
VA loans : no strict DTI cap at all. They use residual income instead (money left over after all debts). We've seen DTIs north of 70% get approved on VA loans. Not a typo.
Front-end vs. back-end DTI: what's the difference?
This trips people up constantly so here's the plain-English version.
Front-end = just your housing costs ÷ gross income
Everything the new house costs you monthly:
- Principal + interest
- Property taxes
- Homeowners insurance
- HOA (if applicable)
- PMI or MIP (if applicable)
That total ÷ gross monthly income = your front-end DTI.
>
Back-end = housing + ALL other debt ÷ gross income
Same housing number, plus every other monthly debt payment:
- Car loans
- Student loans
- Credit card minimums
- Personal loans
- Child support / alimony
>
Easy way to remember it:
- Front-end = just the house
- Back-end = house + everything else
Why the FHA split matters in real life:
Say you earn $6,000/month and want a $3,200/month housing payment. That's 53% front-end, dead on arrival for FHA. Doesn't matter how low your other debts are. The 47% front-end cap is a hard stop.
Flip it, $2,500 housing payment (41% front-end) plus $800 in car and student loans = $3,300 total = 55% back-end. That can get approved on FHA with strong compensating factors like solid reserves or a good credit score.
Front-end kills deals that back-end alone wouldn't. That's why knowing both numbers matters.
The 6 things that actually move your number
1. Income: gross, not take-home. Self-employed? They average your last 2 tax returns. Exception: if you've been in business 5+ years, some conventional loans can qualify you on just one year of returns.
2. Existing debt: every $400/month car payment costs you roughly $50–60k in buying power. This is the biggest swing factor.
3. Down payment: more down = smaller loan = lower payment. Also eliminates PMI at 20% on conventional.
4. Reserves: this one's underrated. Lenders look at how many months of mortgage payments you have sitting in the bank after closing.
Sitting on 6–12 months of reserves? That's a compensating factor. It can get you approved at a higher DTI when nothing else would. A borrower with 48% DTI and 12 months reserves in the bank will often get approved where someone with the same DTI and 1 month reserves won't.
Reserves can include checking, savings, 401k, investment accounts. Does NOT include the cash you're using for your down payment.
5. Credit score: doesn't just affect approval, affects your rate. There's roughly a $150–250/month difference between a 760 score and a 620 score on a $300k loan. Over 30 years that's real money.
6. Interest rate: rates move daily. A 1% rate change on a $350k loan moves your monthly payment by $200+.
The hidden weapon not many talk about: non-occupying co-borrower*
This is one of the most underused tools in mortgage lending and almost nobody knows it exists.
A non-occupying co-borrower is someone who goes on your loan to help you qualify, but doesn't live in the home. Think parents, a sibling, a close family member.
Here's why it's powerful:
- Their income counts toward your DTI qualification
- Their credit score can strengthen the file
- You stay the primary borrower and owner, it's still your home
- They don't need to be on the deed in most cases
Real world example: You earn $60k and can't quite qualify for the home you want. Your parents co-sign as non-occupying co-borrowers. Their income gets added to the file. Suddenly the numbers work, and they get you out of the basement, that's a win-win.
What to know before you use it:
- Their debt counts too, it's not a free income boost. Lenders add their monthly obligations to the back-end DTI calculation
- Works on FHA and conventional loans. VA doesn't allow it unless the co-borrower is a spouse
- The co-borrower's credit gets pulled and their profile matters, a co-borrower with bad credit or heavy debt can hurt more than help
- They take on legal responsibility for the loan. If you miss payments, it hits their credit too
Used correctly, a non-occupying co-borrower can be the difference between getting into a home now versus waiting another 2–3 years. Most loan officers won't bring it up unprompted, so if you're close but not quite qualifying, ask specifically about it.
Real numbers by income (rough estimates at ~6% rate, 10% down, some existing debt)
| Income | Monthly Payment | Comfortable (36% DTI) | Max Approved (50% DTI) |
|---|---|---|---|
| $50k | ~$1,167/mo | ~$175–200k | ~$240–260k |
| $65k | ~$1,517/mo | ~$230–260k | ~$310–340k |
| $80k | ~$1,867/mo | ~$290–330k | ~$385–420k |
| $100k | ~$2,333/mo | ~$360–410k | ~$480–520k |
| $120k | ~$2,800/mo | ~$430–490k | ~$575–625k |
| $150k | ~$3,500/mo | ~$540–610k | ~$720–780k |
Comfortable = what you can afford without being house poor. Max = what a lender might actually approve. The gap between those two numbers is where people get into trouble.
Your mortgage payment isn't your total housing cost
Your mortgage payment (PITI — principal, interest, taxes, insurance) is the baseline. Most people budget for that and get blindsided by everything on top of it.
What PITI already includes: principal + interest + property taxes + homeowners insurance. PMI gets added here too if you put less than 20% down.
What it doesn't include — and what people forget:
- HOA fees — $0 to $1,000+/mo depending on the property. Required in many condos and communities
- Maintenance — rough rule is 1%-2% of home value per year (~$250/mo on a $300k home). Water heater, roof, HVAC, it adds up. I had a tree branch fall on my fence yesterday, that's a quick $1K.
- Utilities — heating, cooling, water, electric tend to run higher than renting. Budget $250–$1K/mo depending on home size
A $300k home with a $1,900 PITI payment can realistically cost $2,400–2,800/month all-in once you factor in HOA, maintenance, and utilities. Plan for the real number.
The honest advice nobody gives you
Lenders will approve you for more than you should borrow. A 50% DTI conventional approval is possible. Doesn't mean it's comfortable.
Aim for 36–42% DTI in real life even if you qualify for more. The extra buffer means you can handle a job change, a broken furnace, or just... a life.
Quick cheat sheet
- Conventional back-end DTI limit: 50%
- FHA front-end DTI: 47% hard cap
- FHA back-end DTI: 55–57% with compensating factors
- VA: no hard limit — residual income based, 70%+ DTI approvals happen
- Reserves sweet spot: 6–12 months after closing
- Target DTI for comfort: 36–42%
- Get pre-approved before you shop, it's free and tells you your real number
Happy to answer questions. This stuff is genuinely confusing and most of the info online is watered down, or has an agenda to get you to click bait.
*One note on the non-occupying co-borrower section — I know this one tends to spark debate (sorry boomers). It's a legitimate, fully legal loan program that's been around for decades. It's not a loophole or a handout, the co-borrower takes on real legal liability and their full financial profile gets scrutinized. It's simply a tool that exists, and a lot of people don't know about it. Whether you think people should use it is a separate conversation, just sharing that it's an option.
Drew Fisher NMLS #44061 | Pure Rate Mortgage LLC NMLS #2578474, Educational content only, not financial advice, not a commitment to lend.