Mortgage Affordability

Working Backward From Income to a Maximum Home Price

Mortgage affordability is the maximum home price a lender would likely approve, estimated from income, debts, and the “28/36 rule” most U.S. mortgage lenders reference as a starting guideline. Enter your annual income, existing monthly debt payments, down payment, and expected loan terms, and this calculator estimates that maximum home price.

This answers a different question than the Mortgage Calculator: that one tells you the payment for a home price you already have in mind, while this one works backward from your income and budget to estimate what price range makes sense in the first place.

The Formula

The 28/36 rule caps your estimated monthly housing payment at the lower of two limits:

• Front-end ratio: $\text{Front-End Limit} = \vA{\text{Gross Monthly Income}} \times \vC{28\%}$ — housing costs (principal, interest, taxes, and insurance) shouldn’t exceed 28% of your gross monthly income.
• Back-end ratio: $\text{Back-End Limit} = \vA{\text{Gross Monthly Income}} \times \vD{36\%} - \vB{\text{Existing Debts}}$ — all debt payments combined, including housing, shouldn’t exceed 36% of your gross monthly income.

Once that maximum monthly payment is known, the calculator works backward through the standard amortization formula (accounting for your down payment and an estimated property tax + insurance rate) to solve for the home price that produces exactly that payment.

Worked Example

An income of $90,000/year, $\vB{\$300\text{/month}}$ in existing debts, a $40,000 down payment, a 6.5% interest rate, a 30-year term, and an estimated 1.5%/year for property tax and insurance combined:

1. Gross monthly income: $90,000 \div 12 = \vA{7,500}$ dollars.
2. Front-end limit: $\vA{7,500} \times \vC{28\%} = 2,100$ dollars.
3. Back-end limit: $\vA{7,500} \times \vD{36\%} - \vB{300} = 2,400$ dollars.
4. The lower of the two, $2,100, is the binding limit.
5. Solving backward for a home price that produces a $2,100 total payment (principal + interest + tax + insurance) at these terms: about $310,781.

Key Factors to Consider

• This estimate is a starting guideline, not a lender’s actual underwriting decision. Real mortgage approval also weighs credit score, employment history, cash reserves, and the loan program’s own specific guidelines — some lenders approve borrowers above the 36% back-end ratio, especially with strong credit and reserves, while others apply stricter limits.
• Existing debt payments directly shrink the maximum home price, sometimes significantly. A car loan or student loan payment reduces how much room remains under the 36% back-end limit before it becomes the binding constraint instead of the 28% front-end limit — paying down existing debt before applying can meaningfully raise the affordability estimate.
• “Affordable” by the 28/36 rule and “comfortable” for your own budget aren’t necessarily the same number. The 28/36 rule is a widely-used lending guideline, not a personalized budgeting recommendation — some households prefer a lower housing-cost percentage to leave more room for savings, discretionary spending, or other financial goals.
• A larger down payment increases affordability in two ways at once. It directly reduces the loan amount needed for the same home price, and it can also help avoid PMI (typically required below 20% down) — both effects raise the maximum home price this calculator estimates for the same monthly payment limit.

Common Mistakes

• Assuming this figure is a pre-approval offer. It’s a planning estimate based on a widely cited guideline, not an actual underwriting decision — a real lender also weighs credit score, employment history, and cash reserves, and can come out higher or lower.
• Forgetting to update existing debts before re-running the estimate. Paying off a car loan or lowering a credit card balance can meaningfully raise the back-end limit — an outdated debt figure understates how much home is actually affordable.
• Treating the maximum estimate as the target to borrow. The 28/36 rule describes what a lender is likely to approve, not what’s comfortable for every household’s own budget and savings goals.
• Using a flat national average for property tax and insurance. Actual rates vary significantly by location — the combined percentage here is a planning estimate, and a specific address’s real rate can shift the affordable price meaningfully.

Useful to Know

• Already know the home price you have in mind and want the actual monthly payment? Mortgage Calculator works forward from price, rate, and term to a payment.
• Want to see how this home purchase fits alongside your other debts? Debt-to-Income (DTI) Calculator calculates your overall debt-to-income ratio.
• Trying to decide between buying at this price or continuing to rent? Rent vs. Buy Calculator compares both paths side by side.