Bankrate.com has a great little article on how to figure out how much home you can afford to buy.
Of course, this is how much the bank thinks you can afford.
That’s not always the same thing.
Mortgage lenders are chiefly concerned with your ability to repay the mortgage. To determine if you qualify for a loan, they will consider your credit history, your monthly gross income and how much cash you’ll be able to accumulate for a down payment. So how much house can you afford? To know that, you need to understand a concept called “debt-to-income ratios.”
The standard debt-to-income ratios are: The housing expense, or front-end ratio, and the total debt-to-income, or back-end ratio.
The housing expense, or front-end ratio, shows how much of your gross (pretax) monthly income would go toward the mortgage payment. As a general guideline, your monthly mortgage payment, including principal, interest, real estate taxes and homeowners insurance, should not exceed 28 percent of your gross monthly income. To calculate your housing expense, multiply your annual salary by 0.28, then divide by 12 (months). The answer is your maximum housing expense.
Maximum housing expense = annual salary x 0.28 / 12 (months)
The total debt-to-income, or back-end ratio, shows how much of your gross income would go toward all of your debt obligations, including mortgage, car loans, child support and alimony, credit card bills, student loans and condominium fees. In general, your total monthly debt obligation should not exceed 36 percent of your gross income. To calculate your debt-to-income ratio, multiply your annual salary by 0.36, then divide by 12 (months). The answer is your maximum allowable debt-to-income ratio.
Maximum allowable debt-to-income ratio = annual salary x 0.36 / 12 (months)
Complete details: Mortgage Basics – Bankrate.com