Rules to Grow Rich By

4. Your total housing payments should not exceed 28% of your gross income. Total debt payments should come in under 36%.

These guidelines include payment on all loans, such as school and auto loans and credit card debt.
Also remember to take into account other home-related expenses to judge a house's affordability. Property and school taxes, home insurance and energy costs and requirements can vary considerably around the nation. Try to estimate future maintenance costs and work them into your budget. Some homes, especially older ones, may require more regular upkeep than homes built with more modern materials. Roofs, siding and heating, cooling, plumbing, and electric services may have to be replaced within a few years of purchase.

From CNN Money