Most cruise ship staterooms are designed for two people. To make up for lost revenue from addons like drink packages, shore excursions, and other extras, some cruise lines will charge single travelers who book a double occupancy stateroom a single supplement fee on top of the base per person fare.

Single occupancy is more expensive on cruises because of the "Single Supplement," a surcharge that compensates the cruise line for the lost revenue of a second passenger. Cruise lines base their business models on double occupancy, assuming that two people will be in each cabin spending money on profitable "extras" like alcoholic beverages, specialty dining, spa treatments, and shore excursions. When one person occupies a room built for two, the cruise line essentially loses the "onboard spend" of a second guest. Consequently, solo travelers are often charged anywhere from 125% to 200% of the per-person fare. To address the growing solo travel market in 2026, many newer ships (like those from Norwegian, Royal Caribbean, and Virgin Voyages) are being built with dedicated "Studio" or "Solo" cabins that carry no supplement, though these smaller rooms often sell out months in advance due to high demand and limited inventory.