Most people start their home search the same way: they type "how much house can I afford" into Google, plug a few numbers into a calculator, and walk away with a figure that feels official.
The problem? That figure is usually wrong.
Not because the math is broken, but because most online calculators leave out the costs that actually decide your monthly payment. Here's what you should factor in before falling in love with a listing.
The 28/36 rule is a starting point, not an answer.
You've probably heard the classic guideline: spend no more than 28% of your gross monthly income on housing, and no more than 36% on total debt. It's a reasonable benchmark, but it ignores three things that often matter more:
- Your actual debt-to-income ratio. Lenders look at your full DTI, including car loans, student loans, and credit card minimums. If you've got a $600 car payment, your real housing budget shrinks accordingly.
- Property taxes and insurance. These get rolled into your monthly mortgage payment (called your PITI — principal, interest, taxes, insurance). In some Arizona zip codes, taxes and insurance can add $400–$600 to your monthly payment. Most online calculators either lowball this or skip it entirely.
- PMI (private mortgage insurance). If you're putting down less than 20%, you'll likely pay PMI — typically 0.5%–1.5% of the loan amount per year. On a $400,000 loan, that's another $165–$500 a month.
What your real number depends on.
- The honest answer to "how much house can I afford" isn't a single number. It depends on:
- Your credit score (which affects your interest rate)
- Your down payment amount
- The specific property's taxes and insurance
- Which loan program you qualify for (conventional, FHA, VA, etc.)
- How much wiggle room you want in your monthly budget for life
A loan officer can run your actual numbers in about 15 minutes — including the costs the online calculators miss.
The takeaway.
Online calculators are fine for early daydreaming. But before you start touring homes, get an actual pre-approval. That's the only number that means anything to a seller, and it's the only number that reflects what you can really afford.
