A single supplement is a surcharge added to the cruise fare of a passenger traveling alone in a stateroom designed for double occupancy. Traditionally, cruise lines price their cabins based on two people sharing the cost; when a solo traveler books that room, the cruise line loses the revenue from the "missing" second passenger's fare, as well as potential onboard spending on drinks, specialty dining, and excursions. To compensate, lines charge a supplement that can range from 10% to 100% (double the fare) of the standard per-person price. In 2026, many major lines like Norwegian, Royal Caribbean, and Celebrity have introduced dedicated "Studio" or "Solo" cabins to eliminate this fee. However, if you prefer a standard balcony or suite while traveling solo, you will likely still encounter this high-fidelity fee unless you find a specific "Solo Traveler" promotion where the supplement is waived or reduced.