Here's a breakdown:
When to use a comma:
* "Hopefully" is an introductory phrase: If "hopefully" starts a sentence, it usually requires a comma after it.
* Example: Hopefully, the weather will be good for the picnic.
* "Hopefully" acts as an interjection: If "hopefully" is used to express a wish or desire, it's often followed by a comma.
* Example: I'll try my best, hopefully, that will be enough.
When to omit a comma:
* "Hopefully" modifies a verb: When "hopefully" acts as an adverb, it modifies the verb directly and doesn't need a comma.
* Example: He will hopefully finish the project by Friday.
In short, whether or not you need a comma after "hopefully" depends on its role in the sentence. If it's acting as an introductory phrase or interjection, use a comma. If it's modifying a verb, omit the comma.