From the Captains Club information on the Celebrity website:
Looking to take your vacation to the next level? You’re in luck. MoveUp allows you to bid on a stateroom upgrade after you’ve purchased your cruise. As a valued Captain’s Club member your bid gets a bonus boost based on your tier. So, you get more value than what you bid. Classic members get an extra 1% multiplier, Select members get a 2% multiplier, Elite members get a 3% multiplier, Elite Plus members get a 4% multiplier, and Zenith members get a 5% multiplier.