The 28/36 Rule: How Lenders Determine What You Can Afford
Most lenders evaluate your ability to pay a mortgage using two debt-to-income (DTI) ratios known as the 28/36 rule. The front-end ratio (28%) says your total housing cost — including principal, interest, taxes, and insurance — should not exceed 28% of your gross monthly income. The back-end ratio (36%) says your total monthly debt payments, including housing plus car loans, student loans, credit card minimums, and other obligations, should not exceed 36% of gross income.
Here is a worked example with a $90,000 annual salary ($7,500 gross monthly income): the front-end limit is $7,500 × 0.28 = $2,100 maximum housing payment. The back-end limit is $7,500 × 0.36 = $2,700 maximum total debt. If you already pay $500 per month toward car loans and student loans, your housing budget under the back-end rule is $2,200 — but the front-end cap of $2,100 governs since it is lower. With $2,100 available for PITI at 6.75% over 30 years, you could qualify for a home priced at approximately $340,000 with 10% down.
How Lenders Actually Evaluate Your Application
While the 28/36 rule provides a useful framework, lenders look at several additional factors when deciding whether to approve your mortgage and at what rate:
Credit score is one of the most important factors. A score of 760 or above typically qualifies you for the best available rates. Between 700 and 759, you will pay slightly higher rates — often 0.25% to 0.5% more. Between 620 and 699, expect rates 0.5% to 1.5% higher and stricter qualification requirements. Below 620, conventional loans become difficult, though FHA loans accept scores as low as 580 with 3.5% down.
Employment history matters significantly. Lenders want to see at least two years of stable employment, preferably in the same field. Self-employed borrowers typically need two years of tax returns showing consistent income. Gaps in employment must be explained, and recent job changes can complicate the process even if your income increased.
Cash reserves — money left in your accounts after the down payment and closing costs — provide a safety cushion. Most lenders want to see at least two months of mortgage payments in reserve. For higher-priced homes or investment properties, they may require six months or more.
Down Payment and Its Effect on Affordability
Your down payment directly determines how much you need to borrow and whether you will pay PMI. On a $350,000 home, here is how different down payment amounts change the picture:
With 5% down ($17,500), you borrow $332,500, and your monthly P&I at 6.75% is $2,157. Add PMI of roughly $166 to $415 per month. With 10% down ($35,000), you borrow $315,000, pay $2,043 monthly in P&I, and still owe PMI. With 20% down ($70,000), you borrow $280,000, pay $1,816 in P&I, and avoid PMI entirely — saving $166 to $415 per month.
The difference between 5% and 20% down on a $350,000 home is roughly $500 to $750 per month in total housing costs. That gap affects what you can qualify for: with less money down, lenders may approve you for a smaller loan because the higher payment consumes more of your DTI allowance.
Hidden Costs Beyond the Mortgage Payment
The mortgage payment is not your only housing expense. Homeowners face several additional costs that renters do not, and failing to account for them is one of the most common affordability mistakes:
Maintenance and repairs typically run 1% to 2% of the home's value per year. On a $350,000 home, budget $3,500 to $7,000 annually — or $292 to $583 per month. This covers routine upkeep (HVAC servicing, gutter cleaning, appliance replacement) and unexpected repairs (roof leaks, plumbing issues, foundation problems).
Homeowners association (HOA) fees apply to many condos, townhouses, and planned communities, ranging from $100 to $500 or more per month. These cover shared amenities and exterior maintenance but can increase annually and sometimes include special assessments for major projects.
Utilities are often higher for homeowners than renters because houses tend to be larger. Budget $200 to $400 per month for electricity, gas, water, sewer, and trash depending on your location and home size.
Closing costs run 2% to 5% of the home price — $7,000 to $17,500 on a $350,000 home — and must be paid at the time of purchase on top of your down payment.
FHA vs Conventional Loan Requirements
Conventional loans are the most common mortgage type. They require a minimum credit score of 620 (though 740+ gets the best rates), a down payment as low as 3% for first-time buyers, and DTI ratios generally at or below 36% on the back end. PMI is required below 20% down but can be removed once you reach 80% loan-to-value.
FHA loans are insured by the Federal Housing Administration and are designed for borrowers with lower credit scores or smaller down payments. They accept credit scores as low as 580 with 3.5% down (or 500 with 10% down), allow DTI ratios up to 43% or even 50% with compensating factors, and require mortgage insurance for the life of the loan (not just until 80% LTV like conventional). On a $280,000 FHA loan, the upfront mortgage insurance premium is 1.75% ($4,900, usually rolled into the loan) plus an annual premium of 0.55% ($1,540/year or $128/month).
FHA loans are popular with first-time buyers because the qualification requirements are more forgiving, but the lifetime mortgage insurance makes them more expensive long-term than a conventional loan with PMI that eventually drops off.
Common Affordability Mistakes to Avoid
Maxing out your pre-approval amount. Just because a lender approves you for $400,000 does not mean you should spend $400,000. Lenders do not factor in your retirement savings goals, childcare costs, travel budget, or lifestyle preferences. Most financial advisors suggest keeping your housing costs to 25% of take-home pay rather than 28% of gross income.
Ignoring the total cost of ownership. A $2,000 mortgage payment often becomes $2,800 or more when you add property taxes, insurance, maintenance, HOA fees, and utilities. Make sure you can afford the true monthly cost, not just the P&I figure.
Draining your savings for the down payment. Putting every dollar toward the down payment leaves you with no emergency fund. Financial advisors recommend maintaining three to six months of living expenses in reserve after the down payment and closing costs. Without this cushion, one unexpected expense — a job loss, medical bill, or major home repair — could put you in serious financial trouble.
Forgetting about closing costs. In addition to the down payment, closing costs of 2% to 5% must be paid at purchase. On a $350,000 home, that is $7,000 to $17,500 in cash needed on top of your down payment.
How Credit Score Affects Your Buying Power
Your credit score directly impacts the interest rate you receive, which in turn determines how much home you can afford. On a $300,000 loan over 30 years, here is how credit score tiers affect your monthly payment:
A score of 760+ might qualify for 6.25%, giving you a P&I payment of $1,847. A score of 700-759 might get 6.75%, costing $1,946 per month. A score of 660-699 could mean 7.25% and $2,048 monthly. A score of 620-659 might face 7.75% and $2,152 per month.
The difference between the best and worst rates in this range is $305 per month or $109,800 over 30 years. If your credit score is below 740, spending three to six months improving it before applying — by paying down credit card balances, correcting errors on your report, and avoiding new credit applications — could save you tens of thousands of dollars.
Frequently asked questions
What debt-to-income ratio do lenders require?
Most conventional lenders use the 28/36 rule: housing costs should not exceed 28% of gross monthly income (front-end ratio), and total debt payments should stay below 36% (back-end ratio). FHA loans are more flexible, allowing back-end ratios up to 43% or even 50% with compensating factors like large cash reserves or minimal payment increase over current rent.
How much house can I afford on a $75,000 salary?
At $75,000 annually ($6,250/month gross), the 28% front-end rule allows $1,750 for housing. At 6.75% over 30 years with 10% down, this supports a home price of roughly $260,000 to $280,000 depending on local tax rates and insurance costs. Use the calculator above to model your specific scenario with your actual debts and down payment.
Does my down payment affect how much I can borrow?
Yes. A larger down payment reduces the loan amount needed and eliminates PMI at 20%, which frees up more of your DTI allowance for the actual mortgage. Putting 20% down instead of 5% on a $350,000 home eliminates $166 to $415 in monthly PMI, effectively increasing your borrowing capacity by $30,000 to $70,000.
What costs besides the mortgage should I budget for?
Budget for property taxes (0.5% to 2.5% of home value annually), homeowners insurance ($1,400 to $2,500/year), maintenance and repairs (1% to 2% of home value annually), utilities ($200 to $400/month), and possibly HOA fees ($100 to $500+/month). On a $350,000 home, these additional costs can add $800 to $1,500 per month beyond your P&I payment.
What is the difference between FHA and conventional loans?
FHA loans accept lower credit scores (580 vs 620), require smaller down payments (3.5% vs 3-5%), and allow higher DTI ratios (up to 50% vs 36%). However, FHA loans require mortgage insurance for the entire loan life, while conventional PMI drops off at 80% LTV. For borrowers with credit scores above 700 and at least 5% down, conventional loans are usually cheaper long-term.
Can I get approved for a mortgage with student loan debt?
Yes. Student loans count toward your back-end DTI ratio. Lenders use the actual monthly payment shown on your credit report (or 1% of the balance for loans in deferment or income-driven repayment). If you earn $6,000/month and pay $400 in student loans, that leaves $1,760 for housing under the 36% back-end rule. Paying down or refinancing student loans before applying can increase your home buying budget.
What credit score do I need to buy a home?
The minimum depends on the loan type: FHA loans require 580 (or 500 with 10% down), conventional loans require 620, and VA loans have no official minimum but most lenders want 620+. For the best rates, aim for 740 or higher. Each 20-point improvement in your score can reduce your rate by 0.125% to 0.25%, saving thousands over the loan term.
What is the difference between pre-approval and pre-qualification?
Pre-qualification is an informal estimate based on self-reported income and debts — it takes minutes and carries little weight. Pre-approval involves the lender verifying your income, assets, employment, and credit through documentation, resulting in a commitment letter for a specific loan amount. In competitive markets, sellers often require pre-approval before considering an offer.