does a comma go before or after but

It depends on the context in which "but" is being used.

If "but" is used to join two independent clauses (i.e., two complete sentences), then a comma is usually placed before "but." For example: "I wanted to go to the party, but I had to study for my exams."

However, if "but" is used to join two words, phrases, or dependent clauses, then a comma is not necessary. For example: "I like ice cream but not cake."

It's important to note that there are some exceptions and nuances to these rules, and the use of a comma can depend on the specific style guide being followed.