Start with your gross monthly income and debt

The amount you can afford to pay each month for a house depends on how much money comes in before taxes and what you already owe. Most lenders use two numbers to decide: your debt-to-income ratio (how much you owe compared to what you earn) and your housing ratio (how much of your income goes to the house payment alone).

Lenders typically want your total monthly debt payments—credit cards, car loans, student loans, and the new mortgage—to stay below 43% of your gross monthly income. Some lenders will go to 50%, but that leaves less room for emergencies. Your housing payment alone (mortgage, property tax, homeowners insurance, and mortgage insurance if you put down less than 20%) should not exceed 28% of your gross income, though some lenders stretch this to 31%.

If you earn $5,000 a month gross, a 28% housing ratio means your total housing payment should not exceed $1,400. If you already owe $400 a month on other debts, your total debt payments would be $1,800—which is 36% of your income and within the 43% threshold.

Key Takeaways

  • Most lenders cap your total monthly debt at 43% of your gross income, with housing costs alone limited to 28%.
  • Your housing payment includes the mortgage principal and interest, property taxes, homeowners insurance, and mortgage insurance—not just the loan itself.
  • The down payment you can make, your credit score, and current interest rates all change what monthly payment you can afford.
  • A mortgage pre-approval letter from a lender shows you the actual amount they will lend based on your income and debts, not just a calculator estimate.

How property taxes and insurance change your real payment

The mortgage payment itself is only part of what you owe each month. Property taxes vary widely by location—some counties charge 0.3% of the home's value annually, others charge 2% or more. A $300,000 house in a low-tax area might cost $75 a month in property tax; the same house in a high-tax area could cost $500 a month.

Homeowners insurance is required by lenders and typically runs $100 to $300 a month depending on the home's value, location, and your claims history. If you put down less than 20%, you also pay private mortgage insurance (PMI), which protects the lender if you default. PMI usually costs 0.5% to 1% of the loan amount annually, split into monthly payments.

A $300,000 home with a $60,000 down payment (20%) might have a $1,200 mortgage payment, $150 in property tax, $200 in insurance, and $0 in PMI—totaling $1,550. The same home with a $30,000 down payment (10%) might have a $1,350 mortgage payment, $150 in property tax, $200 in insurance, and $150 in PMI—totaling $1,850. The difference is $300 a month, or $3,600 a year.

Interest rates and loan terms shift what you can borrow

The interest rate you receive depends on your credit score, the size of your down payment, the type of loan, and current market rates. A 0.5% difference in interest rate changes your monthly payment by roughly $150 per $300,000 borrowed. If rates rise between now and when you lock in a rate, your affordable purchase price drops.

Loan term also matters. A 30-year mortgage has a lower monthly payment than a 15-year mortgage on the same loan amount, but you pay far more interest over time. A $300,000 loan at 6.5% costs roughly $1,896 a month over 30 years or $2,380 a month over 15 years. The 15-year payment is $484 higher each month but saves you about $200,000 in total interest.

If you can afford the 15-year payment, it builds equity faster and costs less overall. If the 30-year payment is what fits your budget, that is the right choice for your situation. A lender will approve you based on what you can actually pay, not on what builds wealth fastest.

Credit score and down payment size affect your approval and rate

Lenders charge lower interest rates to borrowers with higher credit scores and larger down payments because both reduce the lender's risk. A score of 740 or above typically qualifies for the best rates. A score below 620 may disqualify you from conventional loans, though some lenders offer FHA loans (backed by the Federal Housing Administration) that accept scores as low as 500.

A 20% down payment eliminates PMI and often qualifies you for better rates. A 10% down payment triggers PMI but requires less cash upfront. A 3% down payment (common for first-time buyers) also triggers PMI and may come with a higher interest rate. The trade-off is between having cash available now versus paying less interest and insurance over time.

If your credit score is below 700 or you have recent late payments, you may not may have access to for the best rates even if your income is strong. Waiting 6 to 12 months to improve your score before applying can save you thousands in interest over the life of the loan.

Get a pre-approval letter to know your real limit

Online calculators and rules of thumb give you a starting point, but a pre-approval letter from a lender tells you the actual amount they will lend based on your specific income, debts, credit score, and assets. The letter is not a may provide—the lender will verify everything again before closing—but it shows you what is realistic.

To get pre-approved, you will need recent pay stubs, tax returns from the past two years, bank statements, and a list of your debts. The lender will pull your credit report and may ask for explanations of late payments or large deposits. The process usually takes 24 to 48 hours.

Pre-approval also signals to sellers that you are a serious buyer and can close on time. It protects you from falling in love with a house you cannot actually afford. If the pre-approval letter says you can borrow $400,000 but the house you want costs $450,000, you know immediately that you need to look at less expensive homes or save a larger down payment.

Account for maintenance, utilities, and property taxes rising over time

Your mortgage payment stays the same (on a fixed-rate loan), but property taxes and insurance rise most years. A house that costs $1,500 a month to own today might cost $1,650 a month in five years. If you buy at the absolute top of what you can afford, a 10% increase in taxes and insurance could push you into financial strain.

Homeowners also pay for maintenance and repairs—a new roof, a failing water heater, foundation cracks. The general rule is to budget 1% of the home's purchase price annually for maintenance, though older homes cost more. A $300,000 house should have $3,000 set aside each year, or $250 a month.

If your pre-approval allows a $1,500 housing payment but you also need to cover $250 in maintenance and utilities are $200, your true monthly cost is closer to $1,950. That leaves less room for other expenses. A safer approach is to buy a house where the housing payment alone is 25% of your gross income, not 28%, so you have cushion for rising costs and unexpected repairs.

Frequently Asked Questions

What if my income varies month to month?

Lenders average your income over the past two years if you are self-employed or work on commission. If your income has been rising, they may use a lower average. If it has been falling, they may use an even lower figure. Showing consistent income for at least two years strengthens your application.

Does a co-signer change how much I can borrow?

Yes. A co-signer's income and debts are added to yours for the debt-to-income calculation. If you earn $3,000 a month and a co-signer earns $2,000, the lender sees $5,000 in household income. However, the co-signer is legally responsible for the loan if you do not pay, so they should understand the commitment.

Can I afford a house if I have student loan debt?

Student loans count toward your total debt-to-income ratio, so they reduce how much you can borrow for a mortgage. If you owe $300 a month in student loans and earn $5,000 gross, that $300 is already part of your 43% ceiling. You have $1,850 left for housing and other debts combined, not $2,150.

What happens if I get a raise after I am approved?

A raise after pre-approval does not change your approved amount—the lender locked in your income at the time of pre-approval. However, a raise before you close on the house can strengthen your application if you provide updated pay stubs. After closing, a raise simply gives you more money to put toward the mortgage or other goals.

Should I max out what the lender approves me for?

No. Just because a lender approves you for $450,000 does not mean you should borrow $450,000. Lenders use formulas that assume you have no emergencies and no other goals. If you buy at your maximum approval, a job loss, medical bill, or major repair can force you into default. A safer approach is to buy a house that costs 80% to 90% of your pre-approval amount.