Like any dairy product, herb butter could go bad if it is left out of the refrigerator or freezer. However, leaving butter in the fridge for an enormously long time can also make it go bad. Similar to regular butter, herb butter can last about ½ o ¾ of a year in the freezer. However, that also depends on the herbs. Some herbs last longer than others.
However, for the most part, the shelf life of butter in the freezer is mainly 6 months. The temperature of the refrigerator and freezer also plays a part in this. If the fridge is higher than forty degrees Fahrenheit, then it will expire quicker than a colder fridge. Herb butter can usually last about a month in a fridge.