The real estate market changes daily, and certain local, national or even global events can affect your market value.There could be a recent sale that strengthens or even enhances your position in the marketplace, or a recent sale that hurts your possibility of obtaining the price that you and your agent once considered appropriate.

When a bank requests an appraisal (either for a buyer or for a re-finance) the appraiser is instructed to utilize only up to 6 months of prior sales.  So an appraisal conducted last year on your home is not an appropriate analysis for today.  If you look at my market statistics reports, you'll see that  there are changes weekly, and those changes need to be addressed as they pertain to your home's value. So the short answer is AS OFTEN AS NEEDED. That could be 15 days from the time you list your home, or every 30 days that your home remains unsold.