Typically, Holland America cruises have 2 formal nights on a 7 day cruise, 3 formal nights on a 10 or 11 day cruise and 4 formal nights on a 14 day cruise.
The standard rule of thumb is 2 formal nights for every 7 days of the cruise.
All that being said, things can change on your cruise, the Captain can alter the number of formal nights depending upon the itinerary (decreasing them). This tends to happen on longer cruises – not on 7 day cruises.
Once you are on board, the “On Location” lists the formal nights for the entire itinerary on day one.