To avoid contamination with harmful bacteria, butter should not be left out for more than 2 hours. Salted butter can be left out slightly longer than unsalted varieties.
The risk of foodborne illnesses increases when butter is left out at room temperature for more than 2 hours. Butter should be kept refrigerated at temperatures of no more than 38 degrees Fahrenheit.
The average shelf life of refrigerated butter is 4 months. Butter should be discarded once the expiration date has passed.
Butter can also be stored in the freezer. Butter should not be kept frozen for more than 1 year, and needs to be thawed at room temperature or in the refrigerator before use.