This is over and above your money for the down payment and closing. Your lender wants to see that you're not living paycheck to paycheck. If you have three to five months' worth of mortgage payments set aside, that makes you a much better loan candidate. And some lenders and backers, like the FHA, will give you a little more latitude on other factors if they see that you save a cash cushion.

That money will also help you with maintenance and repair issues that come up when you own a home. While repairs are sporadic, items such as a new roof, water heater or other big-ticket items can hit suddenly and hard.

Improve your chances by: setting aside money every month. A good rule of thumb: on average you'll spend 2.5 percent to 3 percent of your home's value annually on upkeep, repairs and maintenance, says Joseph Gyourko, chairman of the real estate department at the Wharton School of the University of Pennsylvania. If you're buying a $250,000 home, aim to bank $520 to $625 per month.