A single supplement is the surcharge added to the cruise fare of a passenger traveling alone in a stateroom that was designed for use by more than one person. Standard cruise fares are charged per person, based on double occupancy of a cabin. In order to not lose money on solo travelers, cruise lines require a person staying alone in a cabin to pay double the regular fare. In actuality, single supplements can be anything from an additional 10 percent of the rate up to the full 100 percent. The rate of the supplement may in some cases be determined by special sales or even the cabin category chosen.
Luxury and expedition cruise lines often cater to single travelers, offering lower single supplements on select cruises than those of mainstream cruises. Some ships have cabins designed for individuals traveling alone that do not have a single supplement added to the rate.