Duration of the Listing Contract. The listing contract contains the terms under which the real estate agent will perform marketing and selling services and how much commission she is due upon the closing of a sale. The length of the contract can be three months, six months, a year, or any other period you choose. Agents often don’t like taking listings for less than a month because they don’t have enough time to market the house before the listing expires. A six-month listing is average.