Cooked oatmeal will last in the fridge in an airtight container for up to 5 days. I like to keep all of my grains, including steel cut oats and rolled oats in the fridge or freezer. This will prevent molds from forming and keep your grains (flours, rice, etc) fresher longer. u003cbr/u003eu003cbr/u003eDo the smell test, if it looks off, or smells off, throw it away!