Incredibly versatile yet simple to make, tuna casserole has remained popular over the course of decades for good reason. Like most casseroles, tuna casserole is often baked in large quantities, if you find yourself with leftovers you don't want to waste, you should know how long the casserole can keep in the fridge and freezer.

In an airtight container that keeps out bacteria and odors, leftover tuna casserole will last for about four days in the fridge. If you know you won’t be eating all your leftovers within a few days, throw them in the freezer instead, still keeping them in a sturdy airtight container, where they’ll last for about three months.

To reheat tuna casserole from the fridge, take it out of the fridge a half hour in advance, cover it with foil, and bake in a 350 degree F oven for about 30 minutes. To reheat from the freezer, defrost the casserole in the fridge for 24 hours, let it rest at room temperature for 30 minutes, then bake until its internal temperature hits 165 degrees F.