The rocker - who is set to marry Victoria's Secret model Lily Aldridge later this month - knows within a 10-day range when he will tie the knot but does not know the exact date because his fiancee won't tell him.
He said: "You have to ask Lily about the wedding date. She won't tell me. I think it's somewhere between May 10 and May 20, but she won't tell me because I have a big mouth!"
Although Caleb is in the dark about his big day, his brothers and bandmates Nathan and Jared have revealed they have some big plans for the reception.
Jared told People: "It's going to be a very small wedding and then a big party. I think there are only like maybe 25 people or so going to the wedding, but a lot of people will be at the party."
Nathan added: "I'm the best man and they're having lemon custard for their wedding cake."
Lily has been welcomed fully into the Followill family by the band - which also includes the trio's cousin Matthew Followill - with Jared admitting everyone "loves" her.
He said: "We love her! I'm so excited for the wedding. I just hope she invites all of her model friends to the wedding. That's the only reason I'm going."
Lily has previously revealed the pair are having a traditional wedding ceremony, although it was not what she wanted at first.
She said: "My wedding is going to be very traditional. I didn't think at first I wanted that. But now that it's getting closer, traditional is kind of nice."