Mortgage lenders are in the business of lending money. Their approval amount is calibrated to the maximum they're confident you can repay ??? not to the amount that lets you live comfortably, save for retirement, fund emergencies, and have flexibility. Those are your job to figure out.
Being approved for $550,000 doesn't mean you should spend $550,000. This guide walks through the real calculation: what affordability actually means, what the total monthly cost of homeownership is, and how to find your own number ??? independent of what the bank offers.
The Standard Guidelines (and Their Limits)
Two traditional rules of thumb dominate mortgage affordability advice:
The 28/36 Rule
Your housing costs (mortgage payment including taxes and insurance ??? PITI) should not exceed 28% of gross monthly income. Your total debt payments (housing + all other debt) should not exceed 36% of gross monthly income.
The 3× Income Rule
Don't spend more than 3 times your annual household income on a home. At $120,000 household income, that's a $360,000 purchase price.
Both rules are reasonable starting points ??? but they're built for a different era of interest rates and homeownership costs. At 7%+ mortgage rates, a 3× income home may push you well above 28% of gross income in housing costs. Apply them as orientation, not as precise targets.
The True Monthly Cost of Homeownership
The mortgage payment is only part of what you actually pay. Many first-time buyers are surprised by how much the full picture adds up to:
| Cost Component | Example (on a $400,000 home) | Notes |
|---|---|---|
| Principal & Interest | $2,395/month | 30-year fixed at 7%; based on $320,000 loan (20% down) |
| Property taxes | $417/month | Estimate: 1.25% of value annually; varies widely by location |
| Homeowners insurance | $125/month | Roughly 0.4% of value annually; higher in disaster-prone areas |
| PMI (if <20% down) | $0–$240/month | 0.5–1.5% of loan annually; drops off at 20% equity |
| HOA fees | $0–$600/month | Condos and planned communities; varies enormously |
| Maintenance & repairs | $267–$400/month | Budget 1–1.5% of home value annually |
| Utilities (delta from renting) | $100–$300/month | Larger space, older systems, yard care |
| Total monthly cost | $3,304–$4,337+ | Before HOA; varies significantly |
The mortgage payment alone is $2,395. The true all-in monthly cost is $3,300–$4,300. Budgeting only the mortgage payment is one of the most common and painful mistakes first-time buyers make.
The Maintenance Budget: The Line Item Everyone Underestimates
The 1% rule ??? budget 1% of your home's value annually for maintenance and repairs ??? is widely cited and consistently ignored. On a $400,000 home, that's $4,000/year or $333/month. It's not a payment you make every month; it's money that needs to sit in a dedicated account for when the furnace fails, the roof needs repair, or the water heater gives out.
Older homes and homes in extreme climates may need 1.5–2%. New construction may need less initially but not forever. Budget for it from day one ??? the reserves build slowly, but the bills arrive suddenly.
Working Backwards: Finding Your Comfortable Number
Instead of starting with a purchase price and checking if you can afford it, try working backwards from your budget:
- Start with your take-home pay ??? What actually lands in your account each month after all deductions
- Subtract non-housing fixed expenses ??? Car payments, student loans, insurance, subscriptions, childcare
- Subtract savings targets ??? Emergency fund contributions, 401(k) beyond the employer match, other goals
- Subtract discretionary spending ??? A realistic estimate of what you spend on food, entertainment, travel, etc.
- What remains is your housing budget ??? This is the all-in monthly number: PITI + maintenance + utilities delta
- Back out non-mortgage costs ??? Subtract taxes, insurance, maintenance estimate. What's left is your maximum P&I payment.
- Use that P&I to find your loan amount ??? The Mortgage Calculator lets you enter a payment to find the corresponding purchase price at any rate.
Down Payment: How It Changes the Math
| Down Payment | Loan Amount | Monthly P&I (7%) | PMI (estimate) | Total Monthly (P&I + PMI) |
|---|---|---|---|---|
| 5% ($20,000) | $380,000 | $2,529 | ~$190/mo | ~$2,719 |
| 10% ($40,000) | $360,000 | $2,395 | ~$150/mo | ~$2,545 |
| 20% ($80,000) | $320,000 | $2,129 | $0 | $2,129 |
| 25% ($100,000) | $300,000 | $1,996 | $0 | $1,996 |
The 20% down payment eliminates PMI entirely and meaningfully reduces both the loan amount and monthly payment. But depleting all your savings to hit 20% down creates its own risk ??? you may have no emergency fund and no flexibility for the inevitable early repairs. A 10% down payment with PMI plus a healthy emergency fund is often wiser than 20% down with empty savings.
One More Number: Your Debt-to-Income Ratio
Even if your personal budget analysis says you can afford a certain payment, lenders use debt-to-income ratio to set their maximum. For conventional mortgages, most lenders cap back-end DTI at 43–45%. Use our Debt-to-Income Calculator to confirm you're within lender thresholds before applying.
Find Your Number
The Mortgage Calculator shows full PITI payment estimates at any purchase price, down payment, rate, and term — including a complete amortization schedule.
Should You Even Buy Right Now?
Before committing to a purchase, compare the true 5-, 10-, and 20-year cost of buying vs renting in your market -- including opportunity cost on your down payment.