Start with your gross monthly income and the debt-to-income ratio

The most direct way to find your affordability ceiling is to calculate your debt-to-income ratio — the percentage of your monthly income that goes to debt payments. Most mortgage lenders will not lend to you if your total monthly debt (including the new mortgage payment) exceeds 43% of your gross monthly income. Some lenders go up to 50%, but 43% is the standard threshold.

Here is the math: multiply your gross monthly income by 0.43. That number is the maximum total monthly debt payment lenders typically allow. Subtract what you already pay each month on car loans, student loans, credit cards, and other debts. What remains is the maximum mortgage payment you can carry.

For example, if you earn $5,000 gross per month, 43% of that is $2,150. If you already pay $400 monthly on a car loan and $200 on student loans, you have $1,550 left for a mortgage payment. That $1,550 includes not just the loan payment itself, but also property taxes, homeowners insurance, and mortgage insurance — so the actual loan portion will be smaller.

Key Takeaways

  • Your debt-to-income ratio — the percentage of gross income going to all debt — is the primary number lenders use, and most cap it at 43% of monthly income.
  • The mortgage payment itself is only part of what you can afford; property taxes, insurance, and mortgage insurance all count against your limit.
  • Your down payment size directly affects the loan amount and monthly payment, so saving more down payment money lowers the house price you need to afford.
  • A mortgage calculator that includes taxes and insurance gives you a more realistic picture than loan payment alone.
  • Your credit score, savings for closing costs, and existing debt all narrow or widen what lenders will actually offer you, even if the math says you could afford more.

Convert your maximum payment into a house price using a mortgage calculator

Once you know your maximum monthly payment, use a mortgage calculator to work backward to a house price. You will need to input your down payment amount, your expected interest rate, and your local property tax and insurance rates. The calculator will show you the maximum loan amount that fits your payment limit, and from there you can determine the house price.

The reason you need all these inputs is that the same $1,550 monthly payment supports very different loan amounts depending on where you live and what you put down. A 20% down payment on a $300,000 house in a low-tax state with low insurance costs is not the same as a 5% down payment on the same house in a high-tax state. Property taxes alone vary dramatically by location — some states charge under 0.5% of home value annually, others charge over 1.5%.

Most online calculators (from Bankrate, NerdWallet, or your bank's website) let you adjust these variables. Run the numbers with your actual down payment amount and your actual local tax and insurance rates. That output is your realistic affordability number.

Account for the down payment you can actually save

Your down payment size is not just a number lenders prefer — it directly determines how much house you can afford on a given monthly payment. A larger down payment means a smaller loan, which means a smaller monthly payment, which means you can afford a higher purchase price within your debt-to-income limit.

If you have saved $40,000 and are looking at a $300,000 house, that is a 13% down payment. If you have only saved $15,000, you are looking at a 5% down payment on the same house, which means a larger loan, a larger monthly payment, and possibly mortgage insurance added to your bill. Some lenders require 20% down to avoid mortgage insurance; others allow 3% or 5% down but charge you insurance on top.

Be honest about what you have saved and what you can save before closing. Do not assume a gift from family or a bonus that has not arrived yet. The down payment you have in hand now is the one that matters for your calculation.

Factor in property taxes, insurance, and mortgage insurance

Your monthly housing payment is not just the loan payment. It includes property taxes, homeowners insurance, and — if your down payment is less than 20% — mortgage insurance. All three vary by location and situation, and all three count against your debt-to-income limit.

Property taxes are set by your county or municipality and are based on the home's assessed value. They vary wildly: a $300,000 home might cost $200 per month in property tax in one state and $600 per month in another. You can find your local rate by searching "[your county] property tax rate" or asking a local real estate agent.

Homeowners insurance protects the lender's investment and is required by all mortgage lenders. The cost depends on the home's age, location, and replacement value. In areas with high hurricane or wildfire risk, insurance can be $150 to $300 per month. In low-risk areas, it might be $80 to $120. Get a quote from an insurance agent for the specific area and price range you are considering.

Mortgage insurance (PMI) is charged if you put down less than 20%. The cost is typically 0.5% to 1% of the loan amount annually, divided into your monthly payment. On a $240,000 loan, that could be $100 to $200 per month. Once your home equity reaches 20%, you can usually request to have PMI removed.

Check what interest rate you might actually receive

Your interest rate affects your monthly payment more than almost anything else. A 0.5% difference in rate can change your monthly payment by $100 or more on a $300,000 loan. Before you settle on an affordability number, get a rate quote from at least one lender.

Your credit score is the primary factor lenders use to set your rate. If your score is above 740, you will likely receive the lowest advertised rates. If it is between 680 and 740, you will pay slightly more. Below 680, the rate jumps noticeably. You can check your credit score free through Experian, Equifax, or TransUnion, or through your bank or credit card company.

Interest rates also change daily based on market conditions, so do not lock in a specific number until you are ready to make an offer. But getting a rate quote now tells you whether the affordability number you calculated is realistic for your actual credit profile.

Subtract your existing debt to find your true ceiling

The 43% debt-to-income rule includes all your debt, not just the mortgage. If you have car payments, student loans, credit card balances you are paying monthly, or other obligations, those reduce the mortgage payment you can afford.

List every monthly debt payment: car loan, student loans, minimum credit card payments, personal loans, child support, alimony, anything that shows up on your credit report or that you are legally obligated to pay. Add them up. Subtract that total from your 43% threshold. What remains is your maximum mortgage payment.

This is why paying down debt before buying a house can meaningfully increase your affordability. Eliminating a $300 car payment frees up $300 of your monthly budget for a mortgage payment, which translates to roughly $60,000 to $80,000 more in house price, depending on your interest rate and location.

Build in a buffer for the costs that come after closing

Affordability is not just about the monthly payment — it is also about whether you have money left over after you buy. Homeownership costs money beyond the mortgage: maintenance, repairs, utilities, and the unexpected. A roof leak, a furnace failure, or foundation work can cost thousands.

A common rule of thumb is to budget 1% of the home's purchase price annually for maintenance and repairs. On a $300,000 home, that is $3,000 per year, or $250 per month. If your affordability calculation leaves you with no cushion in your monthly budget, you are buying at the absolute ceiling and have no room for emergencies.

Consider what you can actually afford to live on after the mortgage, taxes, insurance, and utilities are paid. If the answer is "barely anything," the house is too expensive, even if the lender says it is not.

Frequently Asked Questions

What if I have a co-borrower — does that change the calculation?

Yes. Lenders add both incomes together to calculate your debt-to-income ratio. If you earn $4,000 per month and your co-borrower earns $3,000, your combined gross income is $7,000. The 43% threshold applies to that combined number. However, both of your debts count against the limit, so if your co-borrower has significant student loans or credit card payments, that reduces the mortgage payment you can carry together.

Does my credit score affect how much I can afford?

Your credit score does not change the debt-to-income calculation itself, but it changes the interest rate you receive, which changes your monthly payment. A higher score gets you a lower rate, which means a lower monthly payment on the same loan amount — so you can afford a higher purchase price. A lower score means a higher rate and a higher monthly payment, which lowers your affordability ceiling.

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

Yes, but your student loan payments reduce the mortgage payment you can carry. If you are in income-driven repayment and your payment is $0 per month, it does not count against your debt-to-income ratio. If you are paying $200 per month, that $200 comes out of your 43% threshold. Paying down or consolidating student loans before buying can increase your affordability.

What if the lender says I can afford more than I feel comfortable with?

Lenders use the 43% debt-to-income rule because it is a legal standard, not because it is the right number for your life. If the math says you can afford a $400,000 house but you would feel stretched thin, buy the $350,000 house instead. Your comfort matters more than the lender's maximum.

Should I get pre-approved before I start house hunting?

A pre-approval letter from a lender tells you the maximum loan amount they will offer you based on your income, credit, and debts. It is useful because it confirms the affordability number you calculated and shows sellers you are a serious buyer. However, pre-approval is not a promise — the lender will verify everything again before closing, and if your financial situation changes, the offer can be withdrawn.