The Basic Math: Income, Debt, and Down Payment

The amount of house you can afford depends on three things: how much you earn, how much you already owe, and how much cash you have for a down payment. Lenders use these numbers to decide how large a mortgage they will give you, and that mortgage amount sets your ceiling.

Start with your gross annual income — the money you make before taxes. Most lenders will lend you between 2.5 and 3 times your gross income, though some will go higher if your credit is strong and your debts are low. So if you earn $60,000 a year, you might be approved for a mortgage between $150,000 and $180,000. That is the starting point, not the finish line.

Your existing debts shrink this number. Lenders look at your debt-to-income ratio — the percentage of your monthly income that goes to debt payments. Most lenders want this ratio to stay below 43 percent. If you have a car loan, student loans, credit card payments, or child support, those all count. A mortgage payment on top of those existing debts cannot push you over that 43 percent threshold.

Key Takeaways

  • Most lenders will approve you for 2.5 to 3 times your gross annual income, but your existing debts may reduce that amount.
  • Your debt-to-income ratio cannot exceed 43 percent of your gross monthly income when you add a mortgage payment to your other debts.
  • A larger down payment lowers the mortgage amount you need to borrow and improves your approval odds.
  • The price you can afford is not the same as the price you should pay — lenders approve larger mortgages than many households can comfortably manage.
  • Property taxes, insurance, and maintenance costs add 25 to 35 percent to your monthly housing expense beyond the mortgage payment itself.

How Lenders Calculate Your Maximum Mortgage

Lenders use a two-step process. First, they calculate your front-end ratio, which is your housing payment divided by your gross monthly income. Most lenders want this to stay at or below 28 percent. Your housing payment includes the mortgage principal and interest, plus property taxes, homeowners insurance, and mortgage insurance if your down payment is less than 20 percent.

Second, they calculate your back-end ratio, which is all your monthly debt payments — including the new mortgage — divided by your gross monthly income. This is the 43 percent threshold mentioned above. If either ratio is too high, the lender will reduce the mortgage amount they offer you, or deny you altogether.

Here is a concrete example. You earn $5,000 gross per month. Your car payment is $300 and your student loan payment is $200. Your total existing debt is $500 per month. A lender will calculate: $500 divided by $5,000 equals 10 percent. That leaves room for a housing payment of up to $2,150 per month (43 percent of $5,000 minus the $500 you already owe). But the front-end ratio says housing alone cannot exceed $1,400 (28 percent of $5,000). So your housing payment cap is $1,400 per month — the lower of the two limits.

What Your Down Payment Does

Your down payment is the cash you bring to the closing table. It reduces the amount you have to borrow. If a house costs $300,000 and you put down $60,000 (20 percent), you borrow $240,000. If you put down $30,000 (10 percent), you borrow $270,000.

A larger down payment makes you a lower-risk borrower, so lenders approve you more readily and offer better interest rates. It also eliminates private mortgage insurance (PMI), which is an extra monthly fee lenders charge when your down payment is less than 20 percent. PMI typically costs 0.5 to 1 percent of your loan amount per year, split into monthly payments. On a $240,000 mortgage, that could be $100 to $200 per month.

Down payment size also affects which loan programs you can use. Some programs require 3 percent down, others 5 percent, others 10 percent or more. The larger your down payment, the more programs become available to you.

The Difference Between What You Can Afford and What You Should Pay

Lenders approve mortgages based on your ability to make the payment, not on whether that payment leaves you room to live. A lender might approve you for a $400,000 house when a $250,000 house would let you save money, pay for repairs, and handle emergencies.

Financial advisors often recommend spending no more than 25 to 30 percent of your gross monthly income on housing — lower than the 28 percent lenders allow. This gives you breathing room for the costs lenders do not include in their calculation: maintenance, repairs, property tax increases, insurance increases, and utilities.

A useful rule of thumb: if the monthly payment (mortgage, taxes, insurance, and PMI combined) is more than 25 percent of your gross monthly income, the house is probably stretching your budget too far. You can afford it in the lender's eyes, but you may not be able to afford to live in it comfortably.

Costs Beyond the Mortgage Payment

Your monthly housing cost is not just the mortgage. Lenders include property taxes, homeowners insurance, and mortgage insurance in their calculations, but they do not include maintenance, repairs, utilities, or HOA fees — yet those are real costs you will pay.

Property taxes vary widely by location and are set by your county or municipality. In some states they are 0.3 percent of home value per year; in others they are 2 percent or more. Insurance costs depend on your home's value, location, and the insurer. Mortgage insurance (PMI) disappears once you have paid down your loan to 80 percent of the home's original value, but that can take years.

Maintenance and repairs typically run 1 to 2 percent of your home's value per year. On a $300,000 house, that is $3,000 to $6,000 annually, or $250 to $500 per month. Utilities, yard work, and HOA fees (if applicable) add more. A realistic monthly housing cost is often 25 to 35 percent higher than your mortgage payment alone.

Using Online Calculators and Working with a Lender

Online mortgage calculators let you experiment with different income, debt, and down payment amounts to see how they change your approval odds. You can find these on most bank and mortgage lender websites. They are useful for getting a rough sense of your range, but they are not the same as a real pre-approval from a lender.

A pre-approval is a lender's written statement that they will lend you up to a certain amount, based on your actual financial documents. To get pre-approved, you provide pay stubs, tax returns, bank statements, and a credit report. The lender verifies your income, checks your debts, and pulls your credit score. Pre-approval takes a few days to a week and costs nothing.

Pre-approval is different from pre-qualification, which is just a lender's estimate based on what you tell them over the phone. Pre-qualification is faster but less reliable. Once you have a pre-approval letter, you know the actual amount a lender will give you, and you can shop for houses within that range with confidence.

How Credit Score and Interest Rate Affect Your Budget

Your credit score determines the interest rate you will pay on your mortgage. A higher score gets you a lower rate. The difference between a 620 credit score and a 760 credit score can be 1 to 2 percentage points on your interest rate — and that changes your monthly payment significantly.

On a $240,000 mortgage, the difference between a 5 percent interest rate and a 7 percent interest rate is roughly $300 per month. That $300 per month either comes out of your budget or means you can only afford a smaller house. If your credit score is lower than you would like, paying down debt and fixing errors on your credit report before you apply for a mortgage can save you thousands of dollars over the life of the loan.

Interest rates also change with market conditions and the type of loan you choose. A 30-year fixed-rate mortgage has a different rate than a 15-year mortgage or an adjustable-rate mortgage. Lenders will show you the rates available to you based on your credit and the loan type you select.

Frequently Asked Questions

What if I have student loans or other debts I am still paying off?

Those debts count toward your debt-to-income ratio, which reduces the mortgage amount a lender will approve. If you have $300 in monthly student loan payments and $200 in car payments, that $500 comes out of your 43 percent threshold before your mortgage payment is even added. Paying down debts before you apply for a mortgage increases your approval amount.

Does my down payment have to come from my own savings?

Most of it does, but some programs allow gifts from family members. Some first-time homebuyer programs offer down payment help through grants or low-interest loans. The source of your down payment varies by program, so ask your lender what they accept.

What if a lender approves me for more than I think I can afford?

That is common. Lenders approve based on your ability to make the payment, not on whether you will have money left over for emergencies or savings. You can always offer less than your maximum approval amount. Many financial advisors suggest keeping your housing payment to 25 to 30 percent of gross income rather than the 28 percent lenders allow.

How does my interest rate affect how much house I can afford?

A lower interest rate means a smaller monthly payment on the same loan amount, so you can afford a more expensive house. A higher rate means a larger payment, so you can afford less. Interest rates change with market conditions and your credit score, so getting pre-approved shows you the actual rate you will pay.

Can I change my budget after I get pre-approved?

Yes. Pre-approval is not a commitment. You can use it to shop for houses, and if your financial situation changes — you get a raise, pay off a debt, or save more for a down payment — you can ask your lender to recalculate your approval amount.