Bottom line: Lenders use the 28/36 rule: your mortgage payment should not exceed 28% of gross monthly income, and total debt payments should not exceed 36%. These ratios tell you what you can borrow, not what you should spend. The right number for your life depends on your take-home pay, savings goals, and local costs — which lenders do not optimize for.
The most common mistake in home affordability is buying at the top of what a lender will approve. Lender qualification is not a budget recommendation — it is the maximum a lender is willing to lend based on income and debt. It does not account for your retirement contributions, savings goals, childcare costs, or how much you want to spend on things other than housing.
The Lender's Calculation vs. Your Calculation
What lenders use: the 28/36 rule
28% rule: Your total housing payment (principal, interest, property taxes, homeowners insurance, and PMI if applicable) should not exceed 28% of gross monthly income.
36% rule: All debt payments combined (housing + car loans + student loans + credit cards) should not exceed 36% of gross monthly income.
Example: Gross income $8,000/month.
- 28% of $8,000 = $2,240 max housing payment
- 36% of $8,000 = $2,880 max all debt
With $500/month in existing debt (car + student loans), the housing limit under the 36% rule drops to $2,380.
What you should use: the take-home approach
Run the same calculation on your take-home pay (after taxes, retirement contributions, and insurance). Housing at 28% of gross might be 35–40% of take-home — which is very different for your monthly budget.
A more sustainable guideline: housing should not exceed 25–30% of take-home pay. This leaves room for savings, other expenses, and unexpected costs without financial stress.
The Full Cost of Homeownership
Most affordability calculators focus on the mortgage payment. The actual monthly cost of owning a home includes:
| Cost | Typical Range |
|---|---|
| Mortgage principal + interest | Depends on loan size and rate |
| Property taxes | 0.5–2.5% of home value per year ÷ 12 |
| Homeowners insurance | $100–250/month |
| HOA fees (if applicable) | $100–500+/month |
| PMI (if down payment < 20%) | 0.5–1.5% of loan per year ÷ 12 |
| Maintenance reserve | 1–2% of home value per year ÷ 12 |
The maintenance reserve is the most commonly forgotten line item. Homes require ongoing upkeep — roofs, HVAC systems, appliances, plumbing. Budgeting 1–2% of home value per year ($3,500–7,000 on a $350,000 home) prevents large repair bills from becoming financial crises.
- The 28/36 rule is a lender qualification standard, not a personal finance guideline. Many financial planners recommend keeping housing below 25% of take-home pay to preserve savings capacity.
- Property taxes vary dramatically by location — 0.3% annually in Hawaii to 2.5% in New Jersey. On a $350,000 home, that is $1,050 vs. $8,750 per year. Include actual local tax rates in your calculation.
- A $1,000/month difference in your mortgage payment amounts to $360,000 over a 30-year loan. Buying below your maximum approval gives you financial flexibility that compounds significantly over time.
A Practical Affordability Formula
- Take your monthly take-home pay (after all deductions)
- Subtract your savings rate target (e.g., 15% for retirement + emergency fund contributions)
- Multiply the remaining amount by 25–30% to find your maximum comfortable housing payment
- Use a mortgage calculator to find the home price that results in that payment at current rates
Example:
- Take-home: $6,500/month
- Savings target (15%): $975
- Available for lifestyle expenses: $5,525
- Housing at 28%: $1,547/month
- At 7% rate on a 30-year mortgage with 10% down: roughly $215,000 home price
That is significantly less than what the lender might approve at $8,000 gross income. The gap represents financial cushion.
When to Stretch
There are situations where buying toward the top of your range makes sense:
- Strong income growth trajectory (early career in a high-earning field)
- Stable dual income with room to absorb one income loss
- Low cost-of-living area where 28% of gross leaves significant room in take-home
- Exceptional property in a specific location with strong appreciation history
The decision to stretch is not wrong — it is a trade-off between housing and everything else. Make it with a full picture of all the costs, not just the mortgage payment.
Mortgage rates and qualifying standards change frequently. Use current rates and your specific financial details to calculate an accurate affordability estimate.
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