Prepared or cooked mashed potatoes stay fresh and flavorful in the refrigerator for up to four days. Place cooked mashed potatoes in a clean, covered container, and store them in the refrigerator within 2 hours of cooking for best results.
For longer storage, transfer prepared mashed potatoes to a sturdy freezer container, and place in your freezer compartment for up to 4 months. Leave space around the container to allow the potatoes to freeze quickly without thawing other frozen items. Thaw the potatoes in the refrigerator for 24 hours before heating, and reheat in a microwave oven to 165 degrees Fahrenheit. Throw out any leftovers that sit at room temperature for longer than 2 hours.