Channel Divinity: Divine Fortune question

[trumbeller]

This is just a real quick question. Must this ability be used before an attack is rolled, or can it be used once the attack has been rolled, and you've determined that you've missed by one to turn a miss into a hit?

 

[Stalker0]

This is just a real quick question. Must this ability be used before an attack is rolled, or can it be used once the attack has been rolled, and you've determined that you've missed by one to turn a miss into a hit?

The language is a "+1 to your next attack roll or saving throw".

That means that you can't apply it retroactively. As a free action, you can use it whenever you want, but the benefits won't apply until you make that next attack or saving throw.