What "how big" really means: the difference between what you can borrow and what you can pay back

A lender will tell you how much they will lend you. That number is not the same as how much mortgage you can actually afford to pay every month without running out of money for other things. A bank might approve you for a $400,000 loan, but that does not mean a $400,000 mortgage fits your actual life.

The size of a mortgage you can afford depends on three things: how much you earn, how much you already owe, and how much you have saved for a down payment. Lenders use formulas to decide how much to lend. You need to use your own numbers to decide what you can actually pay.

The difference matters because a mortgage is the biggest monthly bill most people have. If you borrow too much, you will have nothing left for car repairs, medical bills, or the month when work is slow. The right mortgage size leaves room for the rest of your life.

Key Takeaways

  • Lenders typically allow a mortgage payment of up to 28 percent of your gross monthly income, but that does not account for your other debts or your actual living costs.
  • Your total monthly debt payments—including the mortgage, car loans, credit cards, and student loans—should not exceed 36 to 43 percent of gross income, depending on the lender.
  • The down payment you have saved directly reduces the size of the loan you need, so a larger down payment means a smaller monthly payment.
  • Your credit score, savings history, and employment record all affect how much a lender will offer, but a lender's offer is not the same as what you can safely afford.

How lenders decide how much to lend you

Lenders use two main ratios to set a ceiling on how much they will lend. The first is called the front-end ratio or housing ratio. It divides your monthly mortgage payment (including property taxes, homeowners insurance, and mortgage insurance if you put down less than 20 percent) by your gross monthly income. Most lenders cap this at 28 percent, meaning your housing payment should not exceed 28 percent of what you earn before taxes.

The second is the back-end ratio or debt-to-income ratio. This divides your total monthly debt payments—mortgage, car loans, student loans, credit cards, and any other regular payments—by your gross monthly income. Most lenders cap this at 36 to 43 percent, depending on the type of loan and the lender. If you already carry a lot of debt, this ratio will limit how much house you can borrow for.

These ratios are starting points, not targets. A lender saying you can borrow $350,000 means you meet their formula. It does not mean $350,000 is the right size for your situation.

The gap between what lenders allow and what you can actually afford

Lender ratios assume you have no other major expenses. They do not account for childcare, medical costs, car repairs, food inflation, or the fact that some months are slower than others. They also assume you will not lose your job, face a health crisis, or need to help a family member.

A safer approach is to work backward from your actual monthly budget. Add up what you actually spend on groceries, utilities, insurance, childcare, transportation, and everything else. Subtract that from your take-home (after-tax) income. What is left is what you can afford to put toward a mortgage payment. Then work with a lender to see what loan size that payment covers.

Many financial advisors suggest keeping your total housing payment—mortgage, taxes, insurance, and mortgage insurance—to no more than 25 to 30 percent of your gross income, which is lower than the lender's 28 percent ceiling. This leaves more room for the unexpected.

How your down payment changes the mortgage size

The down payment is the money you bring to the closing table. If a house costs $300,000 and you put down $60,000 (20 percent), the mortgage is $240,000. If you put down $30,000 (10 percent), the mortgage is $270,000. A larger down payment means a smaller loan, which means a smaller monthly payment.

Down payments below 20 percent trigger private mortgage insurance (PMI), an extra monthly fee that protects the lender if you stop paying. PMI typically costs 0.5 to 1.5 percent of the loan amount per year, added to your monthly payment. This makes smaller down payments more expensive per month, even though the loan itself is smaller.

If you have saved $40,000 and are deciding between a $300,000 house (13 percent down, with PMI) and a $250,000 house (16 percent down, with PMI), the smaller house will have a lower monthly payment and lower PMI costs. The size of mortgage you can afford is partly about how much you have saved.

What happens when you have existing debts

If you carry a car loan, student loans, or credit card balances, those payments reduce how much the lender will approve you for. A $400 car payment and a $200 student loan payment together reduce your borrowing power by roughly $100,000 to $150,000, depending on your income and the lender.

Paying down existing debts before you apply for a mortgage increases your borrowing power and lowers your monthly payment. If you have time before buying, paying off a car loan or credit card can make a real difference in the size of house you can afford.

Some debts, like child support or alimony, are treated the same way. The lender will ask about them and include them in your debt-to-income ratio.

How your income affects the mortgage size

The higher your income, the larger the mortgage a lender will approve. But income is not just your salary. Lenders also count bonuses, commissions, rental income, and income from a second job—though they may average it over two years to account for variation. Self-employed people often have to provide tax returns and profit-and-loss statements to prove their income.

If you are recently employed, changed jobs, or are in a probationary period, lenders may not count all of your income yet. Most lenders want to see at least two years in the same field or with the same employer. If you just started a new job, you may have to wait before applying, or you may only be approved based on your previous income.

A co-borrower—a spouse, partner, or family member—can add their income to yours, which increases your borrowing power. But they also add their debts to the calculation, so this only helps if their income is higher than their debt payments.

The role of your credit score and savings history

Your credit score affects the interest rate you will pay, which changes your monthly payment. A score of 740 or higher typically qualifies for the best rates. A score below 620 may disqualify you from conventional loans, though FHA loans (backed by the Federal Housing Administration) accept lower scores. The difference between a 4 percent rate and a 6 percent rate on a $300,000 loan is roughly $300 per month.

Lenders also look at your savings history. They want to see that you have money in the bank and that you have been saving regularly. A large deposit that appeared suddenly in your account may raise questions. If you received a gift for your down payment, the lender will ask for a letter from the gift-giver stating it does not need to be repaid.

A larger savings cushion—money in the bank beyond your down payment—tells the lender you can handle an unexpected expense without missing a mortgage payment. This can improve your approval odds and sometimes lower your interest rate.

Working with a lender to find your real number

The best way to know what mortgage size you can afford is to talk to a lender before you start house hunting. A mortgage pre-qualification (not a pre-approval) is free and takes 15 minutes. It gives you a rough idea of what you might be approved for based on the information you provide.

A pre-approval is more thorough. The lender will verify your income, check your credit, and review your debts. A pre-approval letter shows sellers that you are serious and that a lender has already said yes to a certain loan amount. Pre-approvals are usually good for 60 to 90 days.

When you talk to a lender, ask them to show you the monthly payment for different loan amounts. Ask what your payment would be at different interest rates, because rates change. Ask what happens to your payment if property taxes or insurance go up. These conversations help you understand the real cost of different mortgage sizes.

Frequently Asked Questions

What if I want to borrow more than the lender will approve?

You cannot borrow more than a lender will lend. If you want a larger house, you need a larger down payment, a higher income, or lower existing debts. Saving more for a down payment is usually the fastest path, because it reduces the loan amount without changing your income or debts.

Does my spouse's income count if we are not married?

No. Only married couples and some domestic partners can combine income on a mortgage application. If you are not married, you can apply together, but the lender will usually base approval on the higher earner's income and both people's debts. Some lenders have different rules, so ask.

Can I get approved for a bigger mortgage if I have a co-signer?

Yes. A co-signer adds their income to the application and takes on legal responsibility for the loan. But they also add their debts to the calculation. A co-signer only helps if their income is significantly higher than their existing monthly payments.

What if my income varies month to month?

Lenders average variable income over two years. If you earn $50,000 one year and $60,000 the next, they will use roughly $55,000. Bonus and commission income may be averaged over three years. Self-employed income is based on tax returns, not what you earned last month.

Should I max out what the lender will approve?

No. A lender's approval is based on a formula, not on your actual life. Borrowing the maximum leaves no room for job loss, medical bills, or home repairs. Most financial advisors suggest borrowing 20 to 25 percent less than the maximum to keep your monthly payment manageable.