I was on the 7 night in November, and they had two formal nights. One on Sunday, and the other on Thursday. Everyone was dressed up on both nights. Some people do not participate, but the majority of the ship does. It varied from women in gowns to cocktail dresses to sunday dresses and men with tuxedos(very few) and suits.
Hope this helps. You are going to love this cruise!!!!
Gorgeous ship!!!!
David