The shelf life of grapefruit can vary depending on a few factors, such as its ripeness, storage method, and type of grapefruit.  Typically, a ripe grapefruit can last up to two weeks if stored in a cool, dry place like the refrigerator.  However, if the grapefruit is not yet ripe, it can take several days to ripen fully and may only last for a few days after ripening. It's essential to check the grapefruit for any signs of spoilage, such as mould, discolouration, or a sour smell, before consuming. If the grapefruit is cut open, it will last 3-5 days in the refrigerator when stored in an airtight container or covered with plastic wrap.  Overall, consuming grapefruit as soon as possible is best to enjoy its maximum flavour and nutritional benefits.