Financial Planning | September 8, 2026 | Capstag.com | 10 min read
How to Calculate How Much House You Can Afford
"How much house can I afford?" has a precise answer, not a feeling. Lenders use a specific formula to decide how much they will lend you — and that same formula is the most reliable tool for deciding how much you should actually spend, regardless of what a lender is willing to approve.
Quick Answer: The standard framework is the 28/36 rule: your total housing payment should not exceed 28% of gross monthly income, and your total debt payments (housing plus all other debt) should not exceed 36%. Calculate both limits, use the lower of the two as your maximum affordable payment, then convert that payment into a maximum loan amount using the mortgage formula. A household earning $120,000/year with $500 in other monthly debt can afford a maximum housing payment of approximately $2,800/month — supporting a home price in the $400,000–$450,000 range depending on interest rate and down payment.
Lenders will often approve you for more house than you should actually buy — their calculation optimises for what you can technically repay without defaulting, not for what leaves you with a comfortable, sustainable financial life. Understanding the affordability formula yourself means you can set your own ceiling, informed by the same math lenders use, rather than accepting whatever number a pre-approval letter hands you. As a finance strategist, this is one of the most consequential calculations most people will ever run — get it wrong, and you spend a decade or more house-poor; get it right, and homeownership remains one component of a healthy financial life rather than its central constraint.
The 28/36 Rule Explained
The 28/36 rule is the standard affordability framework used by most conventional mortgage lenders. It has two components that must both be satisfied:
The 28% front-end ratio: Your total monthly housing payment (principal, interest, taxes, and insurance — PITI) should not exceed 28% of your gross monthly income.
The 36% back-end ratio: Your total monthly debt obligations — housing payment plus all other debt (auto loans, student loans, credit cards, personal loans) — should not exceed 36% of your gross monthly income.
The binding constraint is always the lower of the two calculated limits — you cannot exceed either one independently.
A Fully Worked Example
Household gross annual income: $120,000 ($10,000/month). Other monthly debt payments: $500 (auto loan and student loan combined).
28% limit: $10,000 × 0.28 = $2,800
36% limit: $10,000 × 0.36 = $3,600, minus $500 existing debt = $3,100 available for housing
Binding constraint: The lower of $2,800 and $3,100 is $2,800 — this is the maximum affordable monthly housing payment (PITI) under standard lending guidelines.
From Maximum Payment to Maximum Home Price
Once you know your maximum monthly payment, converting to a maximum home price requires working the mortgage payment formula in reverse, then adding back your down payment, and subtracting the non-P&I portions of PITI (taxes and insurance) to isolate the loan-eligible portion.
Continuing the example: Of the $2,800 maximum monthly payment, estimate property taxes and insurance at approximately $550/month, leaving $2,250/month available for principal and interest. At a 6.5% interest rate over 30 years, a $2,250 monthly P&I payment supports a loan amount of approximately $356,000. Adding a $60,000 down payment: maximum affordable home price ≈ $416,000.
| Annual Income | Max Monthly Payment (28%) | Approx. Max Home Price* |
|---|---|---|
| $60,000 | $1,400 | ~$195,000 |
| $90,000 | $2,100 | ~$310,000 |
| $120,000 | $2,800 | ~$416,000 |
| $150,000 | $3,500 | ~$525,000 |
*Assumes minimal other debt, 6.5% rate, 30-year term, $60K down payment, and estimated taxes/insurance — actual affordability varies by location and personal debt levels.
Why "Approved For" Is Not the Same as "Should Spend": The 28/36 rule represents the outer boundary of what most lenders will approve — not a recommendation for how much to actually spend. Many financial planners suggest targeting well below the 28% ceiling — closer to 20–25% — to preserve room for retirement savings, emergency fund building, and lifestyle flexibility. A household that borrows to the absolute 28/36 limit has little margin for a job loss, medical expense, or interest rate reset on a variable-rate product.
How Debt Changes Your Affordability
| Other Monthly Debt | 36% Limit ($10K income) | Binding Constraint | Max Housing Payment |
|---|---|---|---|
| $0 | $3,600 | 28% rule | $2,800 |
| $500 | $3,100 | 28% rule | $2,800 |
| $1,000 | $2,600 | 36% rule | $2,600 |
| $1,500 | $2,100 | 36% rule | $2,100 |
Notice how the binding constraint shifts from the 28% rule to the 36% rule as other debt increases — at $500 in other debt, the 28% limit is still the tighter constraint, but by $1,000 in other debt, the 36% rule becomes binding and directly reduces the affordable housing payment. This is why paying down existing debt before a home purchase can directly increase your affordable price range, even without any change in income.
Beyond the Ratios: What the Formula Does Not Capture
Regional cost of living. A 28% ratio in a high-tax, high-insurance-cost region leaves a meaningfully different lifestyle than the same ratio in a lower-cost area, since taxes and insurance consume a larger share of the payment before principal and interest are even considered.
Maintenance and repair costs. Standard affordability formulas do not account for the ongoing cost of homeownership beyond PITI — commonly estimated at 1–2% of home value annually for maintenance, repairs, and eventual major system replacements (roof, HVAC, water heater).
Income stability. A dual-income household with stable W-2 employment can reasonably stretch closer to the 28/36 limits than a single-income household or one with variable, commission-based income, where a larger safety margin below the calculated maximum is prudent.
From a Risk Management Perspective: The 28/36 rule is a useful ceiling, not a target. Calculate your maximum using the formula, then deliberately shop below that number — targeting 80-90% of your calculated maximum preserves the flexibility to continue saving for retirement, maintain a full emergency fund, and absorb unexpected expenses without becoming house-poor. The gap between "approved for" and "comfortable with" is where long-term financial stability actually lives.
Conclusion
The 28/36 rule converts "how much house can I afford" from a feeling into a specific, calculable number — your gross income and existing debt determine a maximum monthly payment, which converts directly into a maximum home price at any given interest rate and down payment. Lenders will use this exact formula to determine your pre-approval amount; using it yourself, before you start house hunting, lets you set a realistic and sustainable ceiling rather than discovering your limit only after falling in love with a home outside your comfort zone. Use our free Home Affordability Calculator to instantly calculate your maximum home price based on your actual income, debt, and down payment. For the underlying mortgage payment math this calculation depends on, see our guide on How to Calculate Your Mortgage Payment Without a Calculator.
✅ Key Takeaways
- The 28/36 rule is the standard affordability framework: housing payment should not exceed 28% of gross monthly income, and total debt should not exceed 36%
- The binding constraint is always the lower of the two calculated limits — as existing debt increases, the 36% rule can become the tighter restriction
- A household earning $120,000/year with minimal other debt can typically afford a maximum monthly housing payment of approximately $2,800, supporting a home price around $400,000–$450,000 depending on rate and down payment
- Paying down existing debt before a home purchase can directly increase affordable home price, even with no change in income, by loosening the 36% back-end constraint
- The 28/36 rule represents a lending ceiling, not a spending target — many financial planners recommend targeting well below the maximum to preserve savings capacity and financial flexibility
- Standard affordability formulas do not capture maintenance costs (typically 1-2% of home value annually), regional cost-of-living differences, or income stability — factor these in separately
Frequently Asked Questions
What is the 28/36 rule for home affordability?
The 28/36 rule states that your total monthly housing payment should not exceed 28% of your gross monthly income, and your total debt payments (housing plus all other debt) should not exceed 36% of gross monthly income. Calculate both limits and use the lower of the two as your maximum affordable housing payment — this is the standard framework most conventional mortgage lenders use to determine loan approval amounts.
How much house can I afford on $120,000 a year?
Using the 28/36 rule with minimal other debt, a $120,000 annual income ($10,000/month) supports a maximum monthly housing payment of approximately $2,800. At a 6.5% interest rate over 30 years with a $60,000 down payment, this translates to a maximum home price in the range of $400,000 to $450,000, depending on property taxes, insurance costs, and existing debt levels.
Does existing debt affect how much house I can afford?
Yes, significantly. Existing monthly debt payments (auto loans, student loans, credit cards) directly reduce the amount available under the 36% back-end ratio. As other debt increases, the 36% rule can become the binding constraint instead of the 28% rule, directly lowering your maximum affordable housing payment. Paying down existing debt before a home purchase can meaningfully increase your affordable price range.
Should I borrow the maximum amount a lender approves me for?
Not necessarily. The 28/36 rule represents the outer lending ceiling, not a recommended spending target. Many financial planners suggest targeting well below this maximum — closer to 20-25% of income for housing — to preserve capacity for retirement savings, emergency fund building, and unexpected expenses. Borrowing to the absolute maximum leaves little financial margin if income changes or unexpected costs arise.
What expenses does the 28% housing ratio include?
The 28% front-end ratio is calculated using your total PITI payment: principal, interest, property taxes, and homeowners insurance. It does not include utilities, maintenance, HOA fees, or PMI in the standard formula, though some lenders incorporate PMI and HOA fees into their specific calculations. Always confirm exactly which costs a lender or calculator is including when comparing affordability figures.
This article is for educational purposes only. The information provided reflects general financial principles and does not constitute personalised financial, tax, or legal advice. Always consider your own financial circumstances before making any decisions.
