Every mortgage calculator online will happily tell you the biggest loan a bank might approve. That number is not your answer — it's the ceiling before your life stops fitting inside your house payment. The more useful question is different: given everything else you're already paying for, what monthly housing cost still lets you save, travel occasionally, and cover a surprise car repair without panic?
Start with take-home pay, not gross income
Lenders qualify you against gross income, but you live on what's left after taxes, retirement contributions, and insurance premiums. Run your affordability math against your actual take-home pay, and you'll usually land on a more honest number than any pre-qualification letter provides.
The 28/36 rule is a starting point, not a target
The conventional guideline caps housing costs at 28% of gross monthly income, and total debt payments at 36%. It's a reasonable ceiling for a first pass, but it says nothing about your specific life — childcare costs, a long commute, student loans that end in three years, or a partner's freelance income that varies month to month. Treat 28/36 as the outer edge, then subtract for whatever your household carries that the rule doesn't know about.
Don't forget the costs that show up after closing
Principal and interest are the headline number, but property taxes, homeowners insurance, and — for condos or townhomes — HOA dues can add hundreds of dollars a month that don't show up on the sale price. Older homes often carry higher maintenance reserves too: a roof, water heater, or HVAC system nearing the end of its life is a cost you're inheriting even if it isn't itemized anywhere.
A useful gut check: if covering a $1,500 emergency would require using a credit card, your target monthly payment is probably too high.
Build in a rate buffer
If you're shopping with a pre-approval based on today's rate, ask your lender what the payment looks like a full percentage point higher. Rates move between offer and closing more often than buyers expect, and qualifying comfortably at a slightly worse rate protects you from a payment shock right before you sign.
A simple way to pressure-test your number
- List your current rent or housing cost, then your new estimated payment including taxes and insurance.
- Subtract the difference from your current monthly savings rate — is what's left still enough to hit your other goals?
- Add a placeholder maintenance line, even a rough one: 1% of the home's value per year, divided by twelve.
- Recheck the math at a mortgage rate one point higher than your current quote.
If the number still works after all four steps, you likely have real room, not just approved room. If it doesn't, that's useful information before you fall for a house — better to know now than after the inspection contingency expires.
Where an advisor actually helps
A good advisor won't just show you homes at your maximum approval — they'll ask what you want your monthly cash flow to feel like in year two, after the honeymoon period of a new house wears off. That conversation, more than any spreadsheet, is usually what keeps a purchase from turning into regret.