Do you have to add comma before using the word plus?

The use of a comma before "plus" depends on the grammatical function of "plus" in the sentence.

Here's a breakdown:

* "Plus" as a conjunction: If "plus" is used to join two independent clauses, you do need a comma before it. For example:

* "I went to the store, plus I stopped by the library."

* "Plus" as a preposition: If "plus" is used to introduce a phrase that modifies a noun or verb, you do not need a comma before it. For example:

* "I need to buy groceries, plus some new books."

* "The total cost was $50, plus tax."

* "Plus" as an interjection: If "plus" is used as a stand-alone word expressing an addition, you do not need a comma before it. For example:

* "I'm going to the party, plus I'm bringing my friend."

In general, it's best to err on the side of using a comma before "plus" if you're unsure. It's more likely to be correct than omitting it. However, pay attention to the context to make sure it's grammatically appropriate.