How Much House Can You Actually Afford? The 28/36 Rule

Tier 4 · Big Life Decisions · beginner · ~8 min read · housingmortgagedebtbudgetingbig-decisions

You don’t get approved for a price — you get approved for a payment

Walk into a showing and the first number you see is the price: $350,000, $480,000, $725,000. So it’s natural to think buying a house is about whether you can afford that number. You can’t, directly — almost nobody pays cash. What you can actually afford is a monthly payment, and the price is just whatever that payment happens to buy at today’s interest rate.

This is exactly how a lender sees it, and it’s why two buyers with the same income can be approved for wildly different prices. The lender isn’t really asking “can you afford this house?” It’s asking “can your monthly income comfortably absorb this monthly payment, on top of everything else you already owe?” Get that backwards and you’ll shop in the wrong price range — high or low — for months.

The two ratios that set your ceiling: 28 and 36

Lenders translate “comfortably absorb” into two debt-to-income (DTI) ratios. They’re rules of thumb, not laws, but nearly every conventional loan is sized against them:

• The front-end ratio (≈ 28%). Your housing payment — principal, interest, property tax, and insurance, bundled together and called PITI — should be no more than about 28% of your gross monthly income.
• The back-end ratio (≈ 36%). That housing payment plus every other monthly debt — car loans, student loans, minimum credit-card payments — should be no more than about 36% of gross monthly income.

Your real budget is whichever rule gives the smaller payment. If you carry little debt, the 28% housing rule binds and your income alone sets the ceiling. If you carry a lot, the 36% rule kicks in first, and your other debts eat into the housing budget directly.

Notice the word gross — these are percentages of your pre-tax income, which is part of why the maximum a lender will approve often feels like more than you’d actually want to spend. The bank’s “yes” is a ceiling, not a recommendation.

Working backwards to a price

Here’s the move most buyers never see. Once you know your capped monthly payment, you can run the mortgage math in reverse to find the largest price it buys. Drag the sliders and the simulator does exactly that — it finds your binding DTI cap, subtracts the property tax and insurance baked into PITI, and converts the rest into the biggest loan (and therefore the biggest price) your payment can carry.

Things worth trying

• Start with the default. A $90,000 income, $40,000 saved, $800/month of other debt, at a 7% rate. Read the headline — “Most house you can afford” — and notice the card “What sets your ceiling.” With $800 of monthly debt, it’s the 36% rule: your debts, not your income, are the binding constraint.
• Drag “Other monthly debt payments” to $0. Watch the ceiling jump and the label flip to the 28% income rule. The amber band on the chart — the buying power your debts were costing you — collapses to nothing. That gap is the whole point: every dollar of monthly debt comes straight out of your home budget.
• Now the big one — drag the mortgage rate. Move it from 4% to 8% and watch the curve dive. Your income didn’t change by a penny, but the affordable price can fall by tens of thousands of dollars. You’re buying a payment, and a higher rate buys less house.
• Add to your down payment. More cash down means a smaller loan for the same price — so the same capped payment now reaches a higher price. (It also helps you dodge mortgage insurance once you cross 20% down, a real cost this model keeps simple.)
• Flip the term to a 15-year loan. The affordable price drops. A shorter loan has a higher monthly payment per dollar borrowed, so the same payment budget buys less house — the trade-off for paying far less interest over the life of the loan.

The hidden lever: why the rate matters as much as the raise

Buyers obsess over price and down payment and barely think about the interest rate — yet the rate moves your buying power as hard as anything on the screen. The reason is the same “you’re buying a payment” logic: your monthly budget is fixed by the DTI rules, and the rate decides how much house that fixed payment can finance.

At the same income, a jump from a 4% rate to a 7% rate can cut the price you qualify for by 20% or more. That’s why a rate lock matters, why “marrying the house, dating the rate” (refinancing later if rates fall) is a real strategy, and why buying down your rate with points can be worth more than it looks. The curve on the chart is this effect: drag the rate and you slide along it, your dot dropping with every tick.

The other lever: your existing debts are a tax on your house

The 36% rule has a blunt consequence: a monthly debt payment doesn’t just cost its own dollars — it shrinks the house you can buy. A $400 car payment isn’t only $400 a month; it also lops a chunk off your housing budget, which at today’s rates can mean tens of thousands of dollars less house. The simulator names that number directly: “Your debts cost you.”

This is one of the most useful things to know before you shop. Paying off a car loan or knocking out a credit-card balance can do more for your buying power than months of extra saving — because it lifts the back-end ceiling and frees that payment back into your housing budget. If the “What sets your ceiling” card says the 36% debt rule, your fastest path to more house is usually less debt, not more income. (This is the same dollar-for-dollar logic behind debt payoff strategies and good debt vs. bad debt.)

”Approved for” is not “should spend”

The maximum a lender approves is the most they’ll let you borrow, computed from gross income — not the amount that leaves you comfortable. Stretch to the top of the 36% ceiling and you can end up house poor: technically able to make the payment, but with nothing left for retirement saving, emergencies, or the surprise repairs that come with owning. A roof, a water heater, and a furnace don’t care about your DTI.

A few guardrails that sit inside the lender’s ceiling:

• Budget off take-home, not gross. The 28/36 rules use pre-tax income; your actual cash flow is smaller. A payment that’s 28% of gross can be a much bigger slice of what lands in your account. (See income and take-home pay.)
• Keep the emergency fund intact. Don’t drain it for the down payment; homeownership raises the size of emergency you should plan for.
• Leave room for the costs the payment hides — maintenance (a rough rule is ~1% of the home’s value a year), higher utilities, HOA dues, and furnishing the place.

The honest target for most people is comfortably under the maximum, not at it.

The honest fine print

This simulator is a teaching model, so it keeps a few things deliberately simple:

• It uses the classic 28% / 36% ratios. Real limits vary by loan type, credit score, and lender — some programs stretch the back-end ratio well past 36% — so treat the output as a well-grounded estimate, not a pre-approval.
• PITI includes property tax and insurance, but not PMI or HOA. If you put less than ~20% down you’ll usually pay private mortgage insurance, and many homes carry HOA dues; both count toward the ratios and would lower the price shown here.
• It works off gross income (as lenders do) and assumes your existing debts stay put. Pay them down before you shop and the ceiling rises — that’s the lesson, not a rounding error.
• The property-tax and insurance rates are adjustable because they vary enormously by location. A high-tax area genuinely shrinks how much home a given payment buys — try dragging the tax slider up and watch the price fall.

The takeaway

• You don’t get approved for a price; you get approved for a payment, and the price is whatever that payment buys at today’s rate.
• Two ratios set the ceiling: housing ≤ 28% of gross income (front-end) and housing + all debt ≤ 36% (back-end). The lower one is your real budget.
• The interest rate is a hidden lever — at the same income, a few points can swing your affordable price by tens of thousands of dollars.
• Existing debt is a tax on your house: through the 36% rule, every monthly payment you carry shrinks the home you qualify for, often by far more than the payment itself.
• The lender’s maximum is a ceiling, not a target. Buy comfortably under it and budget off take-home pay, so you own the house instead of the house owning you.

Key terms

• PITI — Principal, Interest, Taxes, and Insurance: the four parts of a housing payment that the 28% rule caps. (PMI and HOA dues, when they apply, count too.)
• DTI (debt-to-income ratio) — your monthly debt payments divided by gross monthly income. The front-end ratio counts only housing; the back-end ratio counts all debt.
• Front-end / back-end ratio — the 28% (housing-only) and 36% (all-debt) DTI caps lenders size loans against.
• House poor — able to make the mortgage payment but with little left over for everything else, the result of stretching to the top of the lender’s ceiling.
• PMI (private mortgage insurance) — an extra monthly cost lenders usually require when you put down less than ~20%; it counts toward your ratios and shrinks affordability.

This is the question to answer before rent vs. buy: first find the price a lender (and your budget) can actually support, then decide whether buying beats renting at that price. It builds on income and take-home pay (the gross vs. net distinction the ratios hide) and pairs with debt payoff — because the fastest way to afford more house is often to owe less on everything else. Once you know your number, mortgage points and ARMs are about shaping the payment itself.