The tipping policies for mainstream cruise lines are as follows.

Carnival Cruise Lines

Carnival automatically adds a $12.95 per person, per day, gratuity to onboard accounts for those booked in standard cabins. Those in suites will be charged $13.95 per person, per day. The amount does not apply to passengers younger than 2. An automatic 15 percent gratuity is added to all bar bills and spa services.

Passengers who want to adjust the amount of their auto-gratuity in either direction can do so at the guest services desk. There are two exceptions. According to the line's website FAQs, for "cruises to nowhere" -- short cruises that do not visit a port -- gratuities must be prepaid.

Celebrity Cruises

Celebrity Cruises automatically adds gratuities to the onboard Seapass account. The "suggested" gratuities added to your account will be $14.50 per day, per passenger ($15 for Concierge Class and AquaClass cruisers). Suite passengers will pay $18 per person, per day. If you wish to adjust the amount you pay, this can be done onboard at guest relations.

An automatic 18 percent gratuity is added to all bar bills and spa services.

Costa Cruises

Costa has varied charges based on where you cruise. In Europe, Dubai, the Red Sea, the Indian Ocean and Caribbean cruises departing from non-U.S. ports, there is a charge of 10 euros per person, per day for all cruise lengths. For Caribbean cruises departing from the U.S. and for Far East cruises, there is a charge of $13.50 per person, per day. Passengers in suites pay $16.50 per person, per day.

For world cruises aboard Costa Luminosa, the fee is 10 euros per person, per day. For transatlantic and repositioning cruises, there is a charge of 12.50 euros per person, per day. Finally, for South America cruises and spring transatlantics, the fee is $12.50 per person, per day.

All gratuities are added automatically to each passenger's onboard account. There is no charge for children younger than 4. Passengers 4 to 14 will be charged 50 percent of the gratuities. Be warned -- Costa states that "the service charge is an integral part of the total price of the cruise and therefore the amount cannot be altered." Aside from that, you are not expected or required to tip any extra while onboard.

Cruise & Maritime Voyages

Cruise & Maritime Voyages automatically adds gratuities to the onboard account. A total of £7 per person, per night (£6 per person for cruises greater than 16 nights) will be added and will be distributed to cabin stewards and restaurant staff.

On the line's premium vessel Astor, there is a charge of $12 per person, per night ($10 per person for cruises of more than 11 nights duration).

If you wish to adjust the amount you pay, this can be done by contacting the reception desk toward the end of the cruise. There are no extra service charges.

Cunard Line

Cunard charges $11.50 per person, per day, to the shipboard account of passengers in Britannia accommodations. The amount is $13.50 for passengers in Grill Class accommodations. This charge is for adults and children. To adjust the amount of your automatic tips or to tip independently, see the purser's office.

An automatic 15 percent gratuity is added to all bar bills. Casino dealers and spa personnel do not receive a cut of these fees, so if you utilize these services, consider tipping deserving staff. A 15 percent charge also applies to spa treatments and services.

Disney Cruise Line

Disney Cruise Line's recommended gratuities are $4 per person (adult or child), per day, for the dining room server; $3 per person, per day, for the assistant server; $1 per person, per day, for the head server; and $4 per person, per day, for the room steward.

Tips can either be prepaid up to three days prior to the start of your sailing or will be automatically charged to onboard accounts. To adjust the amount of your automatic tips or to tip independently, see the purser's office.

An automatic 15 percent gratuity is added to bar, beverage, wine and deck service tabs. An 18 percent gratuity is added to spa services. It is suggested that cruisers tip a couple of dollars for room service as it's delivered.

Fred. Olsen Cruises

Gratuities are entirely at the discretion of each passenger. The recommended amount -- £5 per adult passenger, per day, to be divided equally between the cabin stewardesses and waiters -- is added automatically to passengers' onboard accounts toward the end of the cruise, but it can be adjusted at reception at any point during the sailing. There is no charge for children under 12.

Passengers are at liberty to tip staff members personally if they wish to do so, and envelopes for this purpose are available at reception. All bar bill gratuities are included in the cost of the drink.

Holland America Line

Holland America will automatically charge $13.50 per person per day to passengers in interior, ocean-view and balcony cabins and $15 to suite passengers. Gratuities apply to both adults and children. See the front desk if you wish to adjust your automatic gratuities. An automatic 15 percent gratuity is added to bar and dining room wine purchases.

Marella Cruises

Tipping is not expected or required on Marella Cruises, and there are no additional charges or gratuities on drinks. (Note: Beginning in 2019, the entire fleet will be all-inclusive).

MSC Cruises

MSC Cruises' auto-gratuity varies by destination and onboard currency. Amounts are as follows:

Caribbean and South America cruises and eastbound grand voyages: $12.50 per night, per adult, and $6.25 per night for children 3 and older

South Africa cruises and northbound grand voyages: $8 per night, per adult passenger, and $4 per night, per child 3 and older

Westbound and southbound grand voyages: 10 euros per person, per night, and 5 euros per night for children 14 and older.

Europe (Mediterranean, Canaries and Northern Europe) cruises, "Antilles" and "Emirates" voyages of eight nights or less: 10 euros per person, per night, and 5 euros per night for children 14 and older

Europe (Mediterranean, Canaries and Northern Europe) cruises, "Antilles" and "Emirates" voyages of nine nights or more (including grand voyages): 8 euros per person, per night, and 4 euros per night for children 14 and older

MSC does not permit adjustments to the amounts listed above; however, if you deem service unsatisfactory, you can have the charges removed from your onboard account by contacting the Guest Relations manager while onboard. An automatic 15 percent gratuity is added to bar purchases. Gratuities are not added to spa bills, so passengers can tip at their discretion.

Norwegian Cruise Line

Each adult is automatically billed $14.50 per day to support a salary and incentive program for the service staff. Passengers booked in any suite category are billed $17.50 per person per day. Two exceptions are Norwegian Sky and Norwegian Sun. Because they include beverages in the fares, gratuities on these ships are $19.99 per person, per day for those in standard cabins and $22.99 per person, per day for those booked in suites. There is no charge for children younger than 3.

Tipping above and beyond the service charge is not necessary or expected. Also, should you wish to adjust the charges, you must contact the onboard reception desk.

An 18 percent gratuity is added to bar bills, specialty and entertainment dining, and spa services. Norwegian suggests that passengers who use concierge or butler service provide a gratuity "commensurate with the services rendered."

P&O Cruises Australia

P&O Cruises Australia does not automatically add gratuities onto passengers' accounts or spa or bar bills. Cruisers can choose, at their discretion, to reward crew members who offer outstanding service. Travelers who wish to tip can do so by handing cash directly to the crew members they want to thank. Passengers need not carry cash if they don't want to, as they can add the tips to their onboard accounts.

P&O Cruises U.K.

P&O Cruises' fixed-rate tipping -- known as the line's Service Reward programme -- is £6 per person (ages 12 and older), per day. Passengers can adjust this amount while onboard by requesting to do so at reception. P&O does not add gratuities or suggest additional tipping for other services.

Princess Cruises

Princess Cruises automatically adds $13.50 per day to each passenger's account to cover hotel and dining service. Passengers in mini-suites and club class will be charged $14.50 per day, and suite passengers will pay $15.50 per day. The amount is the same for children and adults, and it can be prepaid up to six days prior to the start of your cruise.

You can adjust your automatic gratuities upward or downward, or eliminate them altogether, at the purser's office. A 15 percent gratuity is automatically added to all bar bills and spa services. Casino staff do not receive a cut of auto-gratuities.

Royal Caribbean International

Royal Caribbean automatically adds tips of $14.50 per person ($17.50 for suite passengers), per day to each passenger's onboard bill. The tips, which can also be prepaid, are shared by dining services staff, cabin attendants and other housekeeping personnel. Passengers who opt for RCI's flexible "My Time Dining" must prepay gratuities. Guidelines are the same for all passengers, regardless of age.

Passengers who believe they've received poor service may ask guest services to reduce or remove the automatic tips while on the ship. A 15 percent gratuity is automatically added to all bar bills, including mini-bar, as well as salon and spa services.