Pudding mix is a dry powder that, when combined with milk, creates a thick and creamy dessert. Most pudding mixes have a shelf life of about 18 months, but this can vary depending on the brand. Once pudding mix is mixed with milk, it should be consumed within 24 hours for best results.
If you have instant pudding mix that is past its expiration date, you may still be able to use it if it has been stored properly. If the mix appears to be clumpy or discolored, it should not be used. When in doubt, throw it out!