(I) can't rightly say.
Rur. I do not know with any certainty. Fred: When do you think we'll get there? Bill: Can't rightly say. Bob: Okay, how does this look to you? Bill: I can't rightly say. I've never seen anything like it before.
I don't rightly know.
Rur. I do not know. Tom: When will Joe be getting back? Charlie: I don't rightly know. Jane: What's the difference between a first cousin and a first cousin once removed? Mary: I don't rightly know.