Potato salad keeps for an average of three to four days in the refrigerator. This time can vary based on other factors, including what type of mayonnaise was used and whether the potato salad was kept without refrigeration for any length of time.
Potato salad made with homemade mayonnaise does not last as long as potato salad made with commercially produced mayonnaise. Mass-produced mayonnaise brands are pasteurized and contain preservatives, which is not necessarily true of homemade mayonnaise. If the potato salad has been left out of the refrigerator for any length of time, such as leftovers from a meal, it should be used within one day.