What lenders will let you borrow versus what you can actually pay

A lender will tell you the maximum mortgage payment they will finance based on your income and debt. That number is not the same as what you can afford. Lenders use formulas that assume you have no other financial goals—no emergency fund, no retirement savings, no room for a job loss or medical bill. Your actual affordability depends on your full financial picture, not just what a bank's calculator says.

Most lenders use two debt-to-income ratios to set their lending limit. The first ratio, called the front-end ratio, allows your housing payment (mortgage, property tax, insurance, and homeowners association fees) to be up to 28 percent of your gross monthly income. The second ratio, called the back-end ratio, allows your total monthly debt payments—including the mortgage, car loans, student loans, credit cards, and other obligations—to be up to 36 to 43 percent of your gross monthly income, depending on the lender and loan type. These are the ceilings. You can borrow less, and often should.

Key Takeaways

  • Lenders calculate affordability using debt-to-income ratios, but these formulas do not account for savings, emergencies, or life changes.
  • The 28 percent front-end ratio means your housing payment should not exceed 28 percent of your gross monthly income; the 36 to 43 percent back-end ratio includes all debt.
  • A realistic affordability number leaves room for property taxes, insurance, maintenance, and unexpected costs that the mortgage payment alone does not cover.
  • Your down payment size, interest rate, and loan term all change the monthly payment for the same home price, so comparing these factors matters more than comparing home prices alone.

How to calculate what the lender will let you borrow

Start with your gross monthly income—the amount you earn before taxes and deductions. Multiply that number by 0.28 to find the maximum housing payment a lender will allow under the front-end ratio. Then multiply your gross monthly income by 0.36 (or up to 0.43, depending on the lender) to find the maximum total debt payment allowed under the back-end ratio. Subtract your existing monthly debt payments from that second number. The result is the maximum new mortgage payment the lender will permit.

Example: You earn $5,000 gross per month. The front-end limit is $5,000 × 0.28 = $1,400. The back-end limit is $5,000 × 0.36 = $1,800. You currently pay $300 per month on a car loan and $150 on student loans, totaling $450. The back-end calculation leaves room for $1,800 − $450 = $1,350 in new housing debt. Your lender will cap your mortgage payment at the lower of the two: $1,350 per month. That is what the lender will permit, not necessarily what you should commit to.

The difference between the mortgage payment and the total housing cost

The mortgage payment itself—principal and interest—is only part of what you pay each month to own a home. Property taxes, homeowners insurance, and mortgage insurance (if your down payment is less than 20 percent) are rolled into your monthly payment or paid separately. Homeowners association fees, if applicable, are usually separate. None of these are optional.

Property taxes vary by location and are assessed on the home's value. In some states, they run $800 to $1,200 per year per $100,000 of home value; in others, they are much lower. Insurance typically costs $800 to $1,500 per year for a standard home, though it varies by location, home age, and coverage level. Mortgage insurance, required when you put down less than 20 percent, adds 0.3 to 1.5 percent of the loan amount annually, paid monthly. A lender's affordability calculation includes these costs, but you need to know the actual numbers for the specific home and location you are considering, not just the mortgage payment.

Beyond monthly costs, budget for maintenance and repairs. Homeowners typically spend 1 to 2 percent of the home's purchase price annually on upkeep—a $300,000 home might need $3,000 to $6,000 per year for roof repairs, plumbing, HVAC service, and other maintenance. This is not a lender requirement, but it is a real cost that affects whether you can actually afford the home.

How down payment size changes what you can afford

A larger down payment lowers your monthly payment in two ways: it reduces the loan amount, and it eliminates mortgage insurance. A smaller down payment increases both the loan amount and the monthly insurance cost. For the same home price, a 10 percent down payment and a 20 percent down payment result in very different monthly obligations.

Example: A $300,000 home with a 7 percent interest rate and a 30-year loan. With 20 percent down ($60,000), the loan is $240,000, and the principal-and-interest payment is roughly $1,596 per month, with no mortgage insurance. With 10 percent down ($30,000), the loan is $270,000, the principal-and-interest payment is roughly $1,797 per month, plus mortgage insurance of roughly $135 per month, totaling about $1,932. The difference is $336 per month, or $4,032 per year. If your lender's affordability limit is $1,400 per month, the 20 percent down scenario fits; the 10 percent scenario does not.

This means you may be able to afford a higher-priced home by saving for a larger down payment, even if your income stays the same. Conversely, stretching to buy now with a small down payment can lock you into a payment that leaves no room for other expenses or emergencies.

Interest rate and loan term: how they reshape affordability

The interest rate you receive depends on your credit score, the loan type, market conditions, and the size of your down payment. A 0.5 percent difference in rate changes your monthly payment significantly. A 30-year loan has a lower monthly payment than a 15-year loan for the same amount borrowed, but you pay far more interest over time.

Example: A $240,000 loan at 7 percent interest. Over 30 years, the principal-and-interest payment is roughly $1,596 per month, and you pay about $334,600 in total interest. Over 15 years, the payment is roughly $2,245 per month, and you pay about $163,900 in total interest. The 15-year loan saves you $170,700 in interest but costs $649 more per month. If your affordability limit is $1,600 per month, the 30-year loan fits; the 15-year loan does not.

When you are deciding what you can afford, you are really deciding between a lower monthly payment and a higher total cost, or a higher monthly payment and a lower total cost. Neither choice is wrong, but the choice changes what home price you can actually manage.

Building in a safety margin for life changes

Lenders assume you will keep your current income and debt level indefinitely. Real life does not work that way. A job loss, a medical emergency, a spouse's reduced hours, or a child's unexpected needs can shrink your income or increase your expenses. A mortgage payment that consumes 28 to 36 percent of your gross income leaves almost no buffer.

Financial advisors often recommend keeping your housing payment to 25 percent or less of gross income, leaving room for other debt, savings, and unexpected costs. This is tighter than what a lender will permit, but it is closer to what most people can sustain through a difficult year without falling behind. If your lender says you can afford $1,400 per month but your income is $5,000, consider whether you can comfortably pay $1,250 instead. The difference is $150 per month, or $1,800 per year—money that could go into an emergency fund or stay in your pocket if circumstances change.

You also need to know what happens to your payment if interest rates adjust. If you are considering an adjustable-rate mortgage, the initial payment may be lower than a fixed-rate mortgage, but it can increase substantially when the rate adjusts. Lenders typically may have access to you based on the initial rate, not the adjusted rate. Make sure you can afford the payment at the higher rate before committing.

The real affordability question: what can you sustain?

Affordability is not a number a lender calculates for you. It is a number you decide based on your own financial goals and risk tolerance. A lender will tell you the maximum they will finance. You need to decide what you are willing to commit to each month for the next 15 to 30 years, accounting for taxes, insurance, maintenance, emergencies, and the possibility that your income or circumstances will change.

Start by listing your monthly expenses: utilities, food, transportation, insurance, childcare, student loans, and anything else you pay for regularly. Add a line for savings—even $200 or $300 per month makes a difference. Then add a line for maintenance and unexpected costs. Subtract all of this from your gross monthly income. What remains is the realistic maximum you should commit to a housing payment. If that number is lower than what a lender says you can afford, trust your own math. You are the one who has to pay it.

Frequently Asked Questions

What if I have a variable income or work on commission?

Lenders typically average your income over the past two years, or use your most recent year if it is lower. If your income fluctuates, budget based on a conservative estimate—the amount you are confident you will earn in a slower year, not your best year. This protects you if work slows down.

Does my credit score affect how much I can afford?

Your credit score affects the interest rate you receive, which changes your monthly payment. A higher score usually means a lower rate and a lower payment for the same loan amount. It does not directly change the debt-to-income ratio a lender will allow, but the lower payment it produces means you can afford a higher-priced home.

Should I use a mortgage calculator to figure out affordability?

Mortgage calculators show you the monthly payment for a given loan amount, rate, and term. They are useful for comparing scenarios, but they do not account for property taxes, insurance, maintenance, or your other financial goals. Use a calculator to see how different down payments or interest rates change the payment, then add in the real costs for the specific home and location you are considering.

What if I can only afford a payment that is higher than 28 percent of my income?

Some people do carry housing payments above 28 percent of income, especially in high-cost areas. If this is your situation, make sure you have a solid emergency fund, minimal other debt, and stable income. The higher your housing payment relative to income, the less room you have for unexpected costs or income loss.

Can I afford a home if I am still paying off student loans or a car?

Yes, but your existing debt payments reduce the mortgage payment a lender will permit under the back-end ratio. If you owe $300 per month on student loans and $250 on a car, that $550 comes out of your total debt allowance. Paying down these debts before you buy increases the mortgage payment you can afford without changing your income.