The 28/36 Mortgage Rule Explained Simply (And When to Ignore It)

The 28/36 rule is the back-of-envelope math lenders use to decide if you can afford a mortgage. It's older than you are (the rough rule dates to mid-20th century banking) and it's still in active use by every major US lender. Knowing how it works lets you back into what house price you'll be approved for before talking to a lender, and more importantly, lets you spot the gap between qualifying for a mortgage and actually being able to afford one comfortably. Here's the math and the cases where the rule fails you.

Last updated: May 2026

The Rule in 10 Seconds

• 28%: housing costs (PITI: principal, interest, taxes, insurance) should not exceed 28% of your gross monthly income.
• 36%: total monthly debt payments (PITI plus car loans, student loans, credit cards, etc.) should not exceed 36% of your gross monthly income.

If both ratios fit, lenders consider you a comfortable mortgage candidate. If only one fits but not the other, you'll get scrutinized. If neither fits, your loan likely gets declined unless you have other strong factors (high credit score, large down payment, strong assets).

The Math With Real Numbers

Example: gross household income of $100,000 a year ($8,333 a month).

• 28% of gross monthly income: $8,333 * 0.28 = $2,333. Maximum monthly housing payment.
• 36% of gross monthly income: $8,333 * 0.36 = $3,000. Maximum total monthly debt payments.

If you have a $400 car payment, your housing budget shrinks to $2,600 ($3,000 total minus $400 car) under the 36% rule. If you also have a $200 student loan payment, housing drops to $2,400.

Working backward to house price:

• Monthly payment cap: $2,400 (after debts)
• Subtract estimated taxes ($350 a month for typical US) and insurance ($150 a month) and HOA if applicable ($150 a month) leaves $1,750 for principal and interest
• At 7% mortgage rate over 30 years, $1,750 monthly P&I supports a loan of roughly $263,000
• With 20% down payment, that supports a home price of $329,000
• With 10% down payment, that supports a home price of $292,000 (with PMI added)

The same household income of $100K supports house prices ranging from $250K to $400K depending on existing debts, down payment, and interest rate. The rule of thumb "3x your annual income" is a rough approximation, but the real number depends heavily on the specifics.

What Counts as "Housing Costs" (PITI)

• Principal: the portion of monthly payment that reduces your loan balance
• Interest: the lender's fee for the money
• Taxes: property taxes, estimated based on the home's assessed value and local tax rate
• Insurance: homeowner's insurance (required by lender), plus PMI if down payment is under 20%

PITI does NOT include:

• HOA fees (lenders count these separately but typically include in the 28% calculation)
• Utilities (electric, water, gas, internet)
• Maintenance (the 1% per year rule of thumb: a $300K house needs $3K a year of maintenance)
• Furnishings and decor
• Closing costs (one-time, separate budget)

Lenders look at PITI plus HOA. Your actual housing cost (PITI + HOA + utilities + maintenance) is roughly 1.4 to 1.6 times PITI. Plan for that, not for PITI alone.

What Counts as "Total Monthly Debt" (the 36%)

• Mortgage PITI
• HOA fees
• Car loans (monthly payment)
• Student loans (monthly payment; if in deferment, lenders typically use 1% of balance as estimated payment)
• Credit cards (the minimum monthly payment, not your full balance)
• Personal loans
• Child support and alimony
• Other recurring debt obligations

NOT counted: utilities, insurance premiums other than home insurance, subscription services, daily expenses.

The Gap Between Qualifying and Affording

Qualifying for a mortgage and being able to afford one comfortably are different. The 28/36 rule is the qualifying bar; the affordability bar is usually 20% to 30% below it. Why:

1. "Gross" vs "net" income

The rule uses gross income (before taxes and deductions). Your take-home is typically 65 to 75% of gross. A $3,000 housing payment that's 28% of gross is more like 36 to 42% of your actual take-home pay. That leaves less for everything else.

2. Hidden housing costs

PITI doesn't include utilities ($150 to $400 a month), maintenance ($150 to $400 a month), or any major repair fund (which you should have). Real housing cost is 1.4 to 1.6x PITI for most homes.

3. Lifestyle expenses

Childcare ($1,000 to $3,000 a month per child in many US markets), retirement savings (you should be saving 10 to 15% of gross), emergency fund building, and discretionary spending all happen in the 64% of income that isn't going to housing or debt. Maxing out the 28% leaves very little for these.

4. Income volatility

If you lose your job or income drops, the mortgage payment doesn't shrink. Buying at 28% with stable W-2 income is different from buying at 28% with variable freelance income.

5. Future life changes

Babies, eldercare, job changes, sabbaticals all cost money. Buying at the top of your 28% budget assumes today's income continues at exactly the same level. It usually doesn't.

The 25/25 Rule (Better for Comfortable Buyers)

A more conservative version that produces more comfortable budgets: housing costs (PITI) should be no more than 25% of TAKE-HOME pay (net), not gross. For a $100K gross income earning $75K net ($6,250 a month), this gives a housing payment cap of $1,562, supporting a home price of around $230K to $270K depending on rates and down payment.

The 25/25 rule is what Dave Ramsey and other personal finance educators recommend. It produces less house but much more breathing room. Most people who have followed the 28/36 rule to the maximum will tell you in retrospect they wish they had bought less house.

3 Cases Where You Should Ignore the 28/36 Rule

Case 1: You're in a very expensive market

San Francisco, NYC, Boston, and other high-cost-of-living areas have median home prices that exceed 5x median income. The 28/36 rule mathematically can't be met by most middle-class buyers. You either rent, buy something much smaller, or stretch beyond 28/36 with eyes open. The rule becomes a warning system rather than a hard limit.

Case 2: You have very high income growth ahead

Medical residents, junior lawyers at top firms, software engineers at promising startups with vesting equity. Current income may be 50% of expected income in 3 to 5 years. The 28% of current income becomes 14% of future income, which is very comfortable. Lenders sometimes account for this with "physician loans" or similar specialized products.

Case 3: You have very large liquid assets

If you have 5 years of expenses in cash plus paid-for assets, the 28/36 rule's risk protection matters less. You can afford to be temporarily "house poor" because your wealth cushion absorbs shocks. This is the case where wealthy buyers sometimes stretch to 35 to 40% of income on housing, knowing they have the assets to backstop.

What Actually Happens in a Lender Conversation

Lenders calculate two key ratios:

• Front-end DTI: proposed housing payment divided by gross monthly income. Should be under 28% for conventional loans; FHA allows up to 31%.
• Back-end DTI: total monthly debt payments divided by gross monthly income. Should be under 36% for conventional loans; FHA allows up to 43%.

Beyond the ratios, lenders look at credit score (740+ unlocks best rates), down payment (20% avoids PMI), employment history (2+ years steady), and reserves (cash equal to 2 to 6 months of payments).

Use the mortgage affordability calculator to see your numbers before talking to a lender. Most people are surprised by how much (or how little) they qualify for compared to what they assumed.

The Pre-Mortgage Workflow

1. Check your credit score. Free at annualcreditreport.com or via your bank or credit card. 740+ is the goal for best rates; 620 is usually the minimum for any conventional loan.
2. Calculate your debt payoff strategy. Use the debt payoff calculator to reduce existing debts before mortgage application. Lower DTI = more house you qualify for AND better rate.
3. Build down payment AND reserves. 20% down avoids PMI. Plus 2 to 6 months of payments in cash reserves makes you a stronger borrower.
4. Get pre-approved BEFORE house hunting. Pre-approval (not pre-qualification) involves a real credit pull and income verification. Sellers take pre-approved buyers seriously.
5. Shop multiple lenders. Rates and fees vary 0.25 to 0.5% between lenders for the same borrower. On a $300K loan, that's $50K+ over 30 years. Get quotes from at least 3 lenders.