Depending on the source, milk should be fine to drink up to a week after the expiration date, according to WebMD. However, there are factors that can determine whether or not milk will spoil before this time. A milk carton that is left out at room temperature will spoil faster, and even a refrigerator that is not cool enough can allow the bacteria that causes milk to spoil to do its work faster.
Many people use the "smell test" to ensure that the milk has not gone off, however, not all bacteria in milk creates an odor. This means that the smell test can still suggest milk is okay, days after the milk has the ability of making someone sick, according to Lifehacker, a website dedicated to tips and downloads for improving work and life techniques. Drinking spoiled milk is rarely a life or death situation for an adult, but it can still cause food poisoning.
These expiration dates are not standardized in the U.S. Milk's expiration dates are usually determined by refrigerating the milk at marginal temperatures, often around 45 degrees Fahrenheit, while refrigerators should be set to about 38 degrees Fahrenheit, according to the Cornell University Milk Quality Improvement Program.