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How Much House Can You Actually Afford? Calculating a Mortgage Payment You Can Handle
A lender will tell you the biggest loan they're willing to give you. That number and the mortgage payment you can actually live with comfortably are often not the same figure.
Ask a bank how much house you can afford and they'll usually tell you the largest amount they're willing to lend. Ask a financial planner and you'll get a smaller, more conservative number. Both are doing correct arithmetic — they're just answering different questions.
Working out the calculation yourself, with your own numbers instead of a lender's maximum, is the only way to know which of those two answers actually fits your life.
The rule most affordability estimates start from
A commonly used starting point is the 28/36 rule: housing costs shouldn't exceed roughly 28% of gross monthly income (front-end ratio), and total debt payments including housing shouldn't exceed roughly 36% (back-end ratio). These are guidelines rather than laws, and many approved loans exceed them, but they're a reasonable place to begin your own estimate before a lender's underwriting gives you a different number.
Step 1: Set your housing budget from income
Maximum monthly housing payment ≈ Gross Monthly Income × 0.28
Step 2: Check it against your other debt
Add your existing minimum debt payments to the proposed housing payment and divide by gross income. If that combined figure is above roughly 36%, the front-end number from Step 1 isn't realistic — reduce the housing payment until the total fits.
A worked example
Gross monthly income: $7,200. Existing debt: a $300 car payment and a $150 student loan payment ($450 total).
Front-end limit: $7,200 × 0.28 = $2,016 Back-end check: ($2,016 + $450) ÷ $7,200 = 34.3% — within the 36% guideline, so $2,016 is a workable starting ceiling for the total monthly housing payment (principal, interest, tax, insurance and HOA).
From monthly payment to loan amount
Once you know the housing payment you can support, work backward to a loan amount using a loan/amortization calculation at your expected interest rate and term, then subtract taxes, insurance and HOA dues from the payment to isolate the amount available for principal and interest. This is the step where the actual mortgage size gets determined, and it's sensitive to the interest rate — the same monthly payment buys a noticeably smaller loan at a higher rate.
What this calculation leaves out
- Maintenance and repairs, commonly estimated at roughly 1% of the home's value per year, are not part of the mortgage payment but are a real ongoing cost.
- Utilities are typically higher in a larger home than in the rental or apartment you're moving from.
- Private mortgage insurance (PMI) applies on many loans with a down payment below 20% and adds a real monthly cost that a simple principal-and-interest estimate can miss.
- Closing costs and moving costs are one-time expenses that reduce the cash available for a down payment or emergency fund, even though they don't appear in the ongoing monthly figure.
Why the lender's maximum and your comfortable number can differ
A lender's approval is based on your income and existing debt at the moment of underwriting. It does not know about your other financial goals — saving for retirement, a child's education, an irregular income, or simply wanting a cash buffer. Two households with identical DTI ratios can have very different tolerance for a stretched housing payment, which is why the affordability calculation is worth running for yourself, with your own priorities, rather than accepting a lender's ceiling as the target.
A practical way to stress-test the number
Before committing, model the payment against a temporarily reduced income — a job change, a period of reduced hours, or one income lost in a two-income household. If the mortgage payment alongside your other essential expenses doesn't survive that scenario for at least a few months using your savings, the number is worth reducing regardless of what the lender approved.
Adjusting the estimate for a variable income
The 28/36 calculation assumes a stable, predictable gross income. For a freelancer, a commissioned salesperson, or anyone with variable income, lenders often average income over the past two years rather than using the most recent month, and it's worth doing the same in your own estimate — basing a housing budget on a single unusually strong month overstates what's sustainable in a slower one.
How interest rate changes shift the affordable price, not just the payment
Because the same monthly payment buys a smaller loan amount as interest rates rise, a housing budget calculated at one interest rate can become unaffordable, or newly affordable, purely from a rate change with no change in your income at all. Recalculating the maximum loan amount at a slightly higher rate than the current one is a reasonable way to build in a buffer if you're shopping for a home over several months while rates could move.
A better affordability check than the maximum loan
After calculating the monthly housing ceiling, subtract the costs that are not part of principal and interest, then test the remaining payment against your actual monthly budget. This creates a useful second check: the loan can satisfy a ratio and still leave too little cash for maintenance, savings, insurance, utilities or irregular expenses.
Frequently asked questions
Is the 28/36 rule mandatory?
No. It's a widely used guideline, not a legal requirement. Many approved mortgages exceed one or both ratios, particularly with strong credit, a large down payment, or compensating cash reserves.
Should I use gross or net income for this calculation?
Lenders use gross (pre-tax) income for these ratios, so calculating your own estimate the same way keeps it comparable to what a lender will tell you.
Does this calculation include property tax and insurance?
The 28% housing-cost figure is meant to include the full monthly housing payment: principal, interest, property tax, homeowner's insurance and HOA dues where applicable, not just principal and interest.
Does a lower mortgage payment always mean a more affordable home?
No. A lower payment can still come with higher taxes, insurance, maintenance, commuting costs or other ownership expenses. Compare the full recurring cost.
Why should I stress-test the interest rate?
A higher rate reduces the loan amount supported by the same monthly payment. Testing a higher rate shows how sensitive your planned purchase is to financing assumptions.
Conclusion
A lender's maximum approval and a comfortable mortgage payment are calculated from the same inputs but answer different questions. Run the 28/36 estimate yourself, work backward to a loan amount at a realistic interest rate, and stress-test the result against a temporary drop in income before treating any number as final.
Try the Loan / Installment Calculator to apply this to your own figures.
Figures in this article are illustrative. Results depend on your own rates, fees, taxes and circumstances, and are for educational and planning purposes rather than financial advice.