How Much House Can You Actually Afford

The 28/36 rule is a starting point, not a law

The familiar 28/36 rule is a quick affordability screen. It suggests keeping the proposed monthly housing cost near or below 28% of gross monthly income and all recurring debt payments near or below 36%. “Gross” means before income tax, payroll deductions, health insurance, retirement contributions, and everything else that reduces a paycheck.

Those percentages are useful because they force income, housing, and debt into the same equation. They are not universal approval limits. The Consumer Financial Protection Bureau notes that different loan products and lenders use different debt-to-income ratio limits. Credit profile, cash reserves, down payment, loan type, and underwriting rules can all change what a borrower qualifies for.

That creates two separate questions:

Qualification: What payment might an underwriting system allow?
Affordability: What all-in payment leaves enough cash for saving, repairs, childcare, health costs, and ordinary life?

The mortgage affordability calculator uses 28% and 36% as transparent planning assumptions. Treat its result as a disciplined first estimate, not a preapproval or a recommendation to spend to the limit.

Front-end and back-end ratios

The front-end ratio looks only at the proposed housing payment:

Front-end DTI = total monthly housing cost ÷ gross monthly income

The back-end ratio adds the other recurring debts that appear in underwriting:

Back-end DTI = (total monthly housing cost + other monthly debt payments) ÷ gross monthly income

Other monthly debts commonly include car loans, student loans, personal loans, court-ordered obligations, and minimum credit card payments. Routine spending such as groceries, utilities, phone service, and subscriptions usually does not enter the lender’s DTI calculation. It still enters your real budget—which is exactly why a lender’s number can be higher than your comfortable number.

Suppose a household earns $9,000 gross per month and already pays $750 per month toward non-housing debts.

The 28% front-end screen permits up to $2,520 for housing: $9,000 × 0.28.
The 36% back-end screen permits $3,240 for all debt: $9,000 × 0.36.
Subtracting $750 of existing debts leaves $2,490 for housing.

The lower number controls, so this screen produces a $2,490 monthly housing budget. Paying off a $300 car loan would raise the back-end result by $300; earning another $300 after tax would not have the same underwriting effect because DTI uses gross income.

“Monthly mortgage” means more than principal and interest

A mortgage quote often leads with principal and interest, but affordability depends on the total monthly housing cost. Build that total from:

principal and interest on the loan;
property taxes;
homeowners insurance;
mortgage insurance, when required;
homeowners association or condominium fees; and
any predictable special assessments or location-specific charges.

Property taxes and insurance are not fixed for 30 years. They can rise even when the principal-and-interest payment on a fixed-rate mortgage does not. An adjustable-rate mortgage can add another source of change. If a calculator omits taxes, insurance, or association fees, its home-price result is incomplete.

A down payment below 20% does not automatically make a purchase unaffordable, but it will often add mortgage insurance to the monthly cost. The exact rules depend on the loan. Price that insurance before increasing the target home price, and keep closing costs separate from the down payment in your cash plan.

Why “approved for” is not “comfortable at”

Underwriting asks whether the loan appears repayable. It cannot fully price your priorities or risks. A lender generally does not know that you plan to have a child, support a parent, replace an aging car, take a lower-paid job, or keep saving 15% for retirement. DTI also ignores much routine spending.

A comfortable payment is therefore a cash-flow decision, not merely a ratio. Start with monthly take-home pay and subtract:

the complete housing payment;
realistic utilities and transportation;
food, healthcare, childcare, and insurance;
minimum debt payments;
retirement and other savings you intend to protect; and
a monthly allowance for maintenance.

There is no single maintenance percentage that fits every property. A new condominium and a 70-year-old detached home carry different risks. Inspect the actual roof, heating and cooling systems, plumbing, exterior, appliances, association finances, insurance exposure, and local labor costs. Then reserve an amount that reflects the property you are buying.

If the plan works only by stopping retirement contributions, carrying future repairs on a credit card, or keeping no emergency fund, the home price is probably too high even if a lender approves it.

Worked example: from income to home price

Continue with the $9,000 monthly gross income and $750 in existing debts. The 28/36 screen capped total housing at $2,490. Now assume:

property tax: $450 per month;
homeowners insurance: $160 per month;
HOA fee: $90 per month;
30-year fixed mortgage rate: 6.5%; and
available down payment: $60,000.

The non-loan housing costs total $700, leaving $1,790 for principal and interest:

$2,490 − $450 − $160 − $90 = $1,790

At 6.5% over 30 years, a $1,790 principal-and-interest payment supports a loan of about $283,200. Adding the $60,000 down payment suggests a home price near $343,200, before accounting for closing costs or mortgage insurance.

That is the ratio-based result—not yet the household’s final budget. Suppose the buyers also want to preserve $900 per month for retirement, $500 for childcare, $400 for home maintenance, and $300 for travel. If the $2,490 housing payment crowds those goals out, they should lower the home-price target and rerun the mortgage calculator, even though the ratios “work.”

Notice how sensitive the answer is. A higher insurance quote, a lower appraisal, a rate change before closing, or a newly financed car can reduce the affordable loan. Use real local estimates as soon as they are available.

Stress-test the payment before shopping

Run at least four scenarios instead of treating one result as precise:

Base case: today’s income, debts, rate estimate, taxes, and insurance.
Higher-cost case: raise property tax, insurance, and maintenance estimates.
Income-shock case: test the payment on one income or a temporarily reduced income.
Rate case: add 0.5 to 1 percentage point to the mortgage rate until it is locked.

Also protect the cash side of the transaction. The down payment is not the only money due at closing, and a buyer who empties every account to close has no buffer for moving, repairs, or the first escrow adjustment. Keep closing costs, immediate repairs, moving expenses, and post-closing emergency savings as separate line items.

Finally, compare multiple Loan Estimates on the same assumptions. Rate, points, lender credits, mortgage insurance, and fees can trade off against one another. The lowest advertised rate is not automatically the lowest-cost or most affordable loan.

Frequently asked questions

Does putting 20% down always make the most sense?

No. Twenty percent may avoid private mortgage insurance on many conventional loans and lowers the amount borrowed, but using every available dollar can leave you cash-poor. Compare the insurance cost and payment savings with the value of keeping an adequate emergency and repair reserve. Loan-specific rules matter.

Should I use gross income or take-home pay?

Use gross income when reproducing lender-style DTI ratios. Use take-home pay for your personal affordability budget. A safe decision needs both views: gross income explains the screening result; take-home pay shows whether the payment fits real cash flow.

Do utilities count in the 28% housing ratio?

Usually the front-end ratio focuses on the mortgage payment, property taxes, homeowners insurance, mortgage insurance, and association dues rather than utilities. But utilities absolutely affect affordability. Estimate them from the property’s size, climate, energy systems, and—when available—the seller’s recent bills.

How accurate is an online affordability calculator?

It is as accurate as its assumptions. Before shopping, a broad estimate is useful. Before making an offer, replace generic figures with a realistic rate quote, local tax records, an insurance quote, association dues, mortgage-insurance pricing, and your full household budget.

Affordability answers whether the purchase can fit the budget; it does not answer whether buying is better than renting for the period you may stay. Make that second decision with the complete rent vs. buy home guide and a property-specific break-even time test.