The printed expiration date on milk is really just a sell by date, and milk is usually still good for a few days after that. Milk should last up to 7 days past the sell-by date if properly refrigerated.
Milk gives off an unpleasant aroma or may become chunky once it has spoiled. Keep the milk in the back of the refrigerator and away from too much light in order to extend its shelf life. Make sure it is stored in its original container and tightly closed. Spoiled milk may cause sickness, so always check if it is spoiled before drinking. Skim milk may last longer than whole milk.