Homemade cottage pie can last for up to three to five days in the fridge when stored properly. It's important to let the pie cool completely before refrigerating, and to cover it tightly with aluminum foil or plastic wrap. When reheating, make sure to heat it thoroughly to an internal temperature of 165°F (74°C). If you have leftovers that won't be eaten within five days, it's best to freeze them for future consumption.