Plain calcium doesn't degrade, so plain Ca can be used 'forever'. The vitamins degrade easily, depending on storage. If you keep the container cool and dry (in the fridge, for example), they should safely last for a year, though some sources say 2 years. I tend to only keep mine for a year. My vitamin containers are stored in the freezer, the powder doesn't freeze, so it's just as easy to use. Check the expiry date on the containers before you buy them. I've seen some stores selling vitamins that expire in a couple of months, or some aleady have expired.