A lender will tell you what you can borrow. That number is often bigger than what you can comfortably afford, and the gap between those two figures is where house-poor comes from.
Getting pre-approved for $450,000 feels like an achievement. It isn't a recommendation. It's an estimate of what a lender believes it can collect, built from your gross income and your reported debts — not from your childcare bill, your retirement contributions, or the fact that your car is nine years old. It's also not final approval: terms can change after underwriting, appraisal, documentation, rate lock, and final approval.
Here's how the standard rules work, what they leave out, and how to find a number that survives contact with your actual life.
Quick answer: Two rules of thumb dominate. The 28/36 rule suggests keeping housing costs near 28% of gross monthly income and total debt payments near 36%. Lenders often allow higher — qualifying decisions commonly hinge on debt-to-income ratio, and many programs permit DTI well above 36%. Both are starting points, not verdicts. The number that matters is what's left after your actual obligations, and the biggest mistake is budgeting for the mortgage payment instead of the total monthly cost — principal, interest, property taxes, insurance, any HOA dues, and mortgage insurance if it applies. That payment can also change over time if taxes, insurance, HOA dues, escrow amounts, or an adjustable rate change.
The Number Lenders Use: Debt-to-Income
Most mortgage decisions run through DTI — your monthly debt payments divided by your gross monthly income.
DTI = total monthly debt payments ÷ gross monthly income
Lenders typically look at two versions: a front-end ratio covering just housing costs, and a back-end ratio covering housing plus every other required monthly debt payment — car loans, student loans, minimum credit-card payments, personal loans. Different loan programs count income, debts, student loans, alimony, child support, and other obligations differently, so a lender's DTI isn't always identical to your back-of-the-napkin calculation.
Two things worth understanding about that formula:
- It uses gross income, not take-home. If a meaningful share of your paycheck disappears to taxes, retirement contributions, and health premiums before you see it, the ratio already overstates what you can handle. (Why your take-home pay looks smaller covers where that money goes.)
- It mainly counts required debt obligations the lender considers, not every real-life expense. Childcare, groceries, medical costs, tithing, supporting a family member, saving for anything — none of it appears. A lender isn't ignoring those expenses out of carelessness; they simply aren't part of the calculation.
If you want to run your own number, how to calculate your debt-to-income ratio walks through it.
The 28/36 Rule, and Why It's a Starting Point
The most cited guideline:
- 28% — keep total housing costs at or below 28% of gross monthly income
- 36% — keep all debt payments at or below 36% of gross monthly income
On $7,000 of gross monthly income, that's roughly $1,960 for housing and $2,520 for all debt combined.
The 28/36 rule is a planning guideline, not a universal underwriting rule. It's a reasonable opening position, and it's conservative relative to what many lenders will approve — FHA, VA, USDA, conventional, jumbo, and portfolio loans can use different rules, costs, and DTI tolerances. Qualifying standards vary by loan program, and plenty of borrowers are approved above these thresholds — which is exactly why the rule is useful as your guardrail rather than a description of the market.
Where the rule strains: high-cost areas, where 28% may be unreachable for anyone; and households with unusual fixed costs, where 28% is still too much. Treat it as a reference point you adjust from, not a law.
What "Housing Cost" Actually Includes
This is the most expensive misunderstanding in the whole process. People budget the mortgage payment and get surprised by the bill.
Your real monthly housing cost typically includes:
| Component | Notes |
|---|---|
| Principal & interest | The part most people mean by "the payment" |
| Property taxes | Vary enormously by location; often escrowed. Can change after purchase, especially on reassessment or if exemptions change |
| Homeowners insurance | Also often escrowed; premiums have risen sharply in some markets, and availability can be an issue in higher-risk areas |
| Flood, wind, or other required insurance | May apply depending on the property and location |
| Mortgage insurance | Common with smaller down payments. Can mean PMI on some conventional loans, mortgage insurance premiums on FHA loans, or guarantee fees on certain government-backed loans |
| HOA or condo dues | Can be substantial, and can increase |
Principal and interest is frequently a minority of the difference between renting and owning once taxes and insurance load on. Two identical houses in different counties can carry meaningfully different monthly costs purely from the tax line.
Utilities can also change meaningfully when you move from an apartment or a smaller home into a larger house.
And then there's the category no calculator shows you: maintenance. Roofs, water heaters, HVAC systems, and appliances fail on their own schedule. A common planning approach is setting aside a percentage of the home's value annually, but the honest version is that it's lumpy and unpredictable — you need a fund, not a monthly line item.
The Affordability Test That Actually Works
Rules of thumb use gross income because lenders do. You don't have to.
Start from what actually lands in your account, then subtract what you're already committed to — not just debts, but childcare, insurance, retirement contributions you don't want to stop, and the saving you'd like to keep doing. What's left is your honest housing ceiling.
Three checks worth running against it:
- Would this survive one lost income? For dual-income households, this is the question that matters most. It doesn't have to be a "yes" forever — but if the answer is no, decide how many months of reserves would make you comfortable.
- Does it still leave room to save? A payment that consumes everything you'd otherwise put toward retirement or an emergency fund isn't affordable; it's a bet that nothing goes wrong.
- Have you tried living on it first? Set aside the difference between your current housing cost and the proposed one every month for a few months. If that's painless, the number is probably real. If it isn't, you learned it for free.
That third one is the most useful exercise in this entire post.
The Costs That Bracket the Purchase
Two more line items people underestimate:
Closing costs. These cover lender fees, title, appraisal, and prepaid items, and they vary by loan type, lender, location, purchase price, down payment, and prepaid amounts. They're due at closing and separate from your down payment. After you apply, the Loan Estimate is the document to review for projected payments, closing costs, cash to close, and whether amounts can change.
Moving in. The house is rarely done. Appliances, window coverings, a lawn mower, the immediate repair the inspection flagged — this reliably runs into the thousands and lands the same month as your largest-ever purchase.
Which leads to the rule that outranks all the ratios: don't drain your emergency fund for the down payment. Closing with nothing behind you means the first surprise goes on a credit card. If you're still building toward the purchase, how to save for a house covers that stretch.
Before You Shop
- Check your credit first. Rate offers depend heavily on credit profile, and reviewing your report early leaves time to fix errors — see how to read a credit report.
- Know the difference between pre-qualification and pre-approval. They're not the same, and lenders use the terms inconsistently. Ask what a given lender means and what it required.
- Compare Loan Estimates side by side, not advertised rates — look at total monthly payment, cash to close, APR, interest rate, points, lender credits, and whether the tax and insurance estimates differ between lenders.
- Shop within a focused window. FICO scoring models generally group properly coded mortgage rate-shopping inquiries within a shopping window — newer versions commonly use 45 days, older ones 14 — though the exact treatment depends on the model. How inquiries work explains it.
- Ask for a full monthly estimate, not just principal and interest: taxes, insurance, mortgage insurance, and any HOA dues.
- Ask about the rate. If you're considering an adjustable-rate mortgage, understand when and how the payment can change. If you're relying on a quoted rate, ask whether it's locked and for how long.
- Decide your number before you look. Touring houses above your ceiling is how ceilings move.
The Bottom Line
Affordability isn't the largest payment a lender will approve. It's the largest payment that still leaves your life intact — retirement contributions continuing, emergency fund untouched, and enough slack that a broken furnace is annoying rather than catastrophic.
Use 28/36 as an opening guardrail, price the total monthly cost rather than the mortgage payment, and test-drive the number for a few months before you commit to it for thirty years. A house you can comfortably afford is worth more than a bigger one you can technically qualify for.
That's what clarity looks like.
The honest version of this calculation starts with what you actually spend, not what you assume you spend. Canopy can help you view supported connected and manually entered accounts, income, bills, spending, debts, goals, and estimated cash flow in one place, so the housing number you land on is built from your real numbers. Canopy does not estimate property-specific taxes, insurance, HOA dues, closing costs, or mortgage terms. Start with Canopy — free, no credit card needed.
Canopy is not a lender, mortgage broker, real estate professional, or financial adviser. It does not originate or underwrite mortgages, pre-qualify or pre-approve you, determine how much house you can afford, estimate property taxes, insurance, or closing costs, quote rates, or guarantee approval or terms. Canopy does not compare lenders, generate Loan Estimates, calculate DTI for underwriting, evaluate loan programs, determine reserves needed, or provide homebuying, mortgage, tax, legal, real-estate, or financial advice.
Related Reading
- What Is Debt-to-Income Ratio? How to Calculate Your DTI
- How to Save for a House in Your 20s and 30s on a Normal Income
- Why Your Take-Home Pay Looks Smaller Than You Think
- How to Read a Credit Report
- How to Calculate Your Net Worth in 5 Minutes
- How to Budget on a Variable Income in 2026