Koufonisia is where many island-hoppers go to do nothing at all: a tiny inhabited island, Ano Koufonisi, with one village, sandy coves and clear water, and an almost empty neighbour, Kato Koufonisi. Mykonos is the opposite, busy, stylish and loud. This crossing is how people swap one for the other, often ending a quiet stretch in the Small Cyclades with a few nights of Mykonos beaches and bars, or heading for Mykonos airport at the end of a trip.
It is a seasonal, high-speed route with a single operator. Seajets runs it from April to October, and every sailing is a fast boat, so there is no cheap conventional option on the direct line. When we checked, the lowest adult fare on Ferryhopper was €85.70; many sailings in its table of last year's data started at €95.70 or €103.70.
Times vary with the routing. In Ferryhopper's monthly figures for this direction, most Seajets sailings took 2 hours 5 to 2 hours 15 minutes, as the boats call at other islands on the way, and the quickest took 1 hour 20 minutes. Our older page for this route described a Blue Star Ferries conventional sailing of up to 2 hours 42 minutes and a May start; Ferryhopper lists neither, so we have dropped them.
Plan the day around the ferry, not the other way round. If you are flying out of Mykonos (JMK), leave a generous buffer, and remember that Mykonos taxis are scarce in summer, so arrange your transfer from the port in advance.