Lenders are careful, but they make qualification decisions based on averages and formulas. They won't understand the nuances of your lifestyle and spending patterns quite as well as you do. So, leave a little room for the unexpected - for all the new opportunities your home will give you to spend money, from furnishings, to landscaping, to repairs.
Historically, banks use a ratio called 28/36 to decide how much borrowers could borrow. An approved housing payment couldn't be more than 28 percent of the buyer's gross monthly income, and his or her total debt load, including car payments, student loans, and credit card payments, couldn't be more than 36 percent. (In Canada lenders apply similar formulas to determine how much a buyer can afford.