I'm an American, so this is strongly biased towards American standards and guidelines—in fact, as Fruan and RPGeek have reminded me, it's pretty much only applicable in the U.S.1 I have very little experience elsewhere, although I recall in Paris my then-girlfriend and I left €1 each on top of the included gratuity. Moreover, I live in New York, so that may further skew the numbers here listed. Naturally, your mileage may vary.
EDIT 10/12/2005: Thomas Keller's Per Se in the Time-Warner Center in New York has recently abolished tipping and added a 20% service charge to all checks.
In all cases, of course, you can adjust these numbers up or down to reflect the quality of the service, but looking for problems in order to justify a lower tip makes baby Jesus cry.
Whatever the guidelines might say, avoid leaving coins, definitely avoid leaving only coins, and even if you're charging the tip, don't tip less than a dollar. If you're paying by credit card but tipping in cash, write "cash" in the line for the tip unless you don't mind getting dirty looks.
If you find yourself in a situation not listed here, 15% to 25% is probably about right.
Lastly, this is purely from the viewpoint of a customer; I've never depended on tips, nor have I held a job where tips were customary.
- At a full-service restaurant, tip about 15% to 20% of your total bill. In large cities, lean towards the 20% end of that range. Your total bill includes all food at all courses, all beverages for which you were charged, alcoholic or not, and all taxes.
- In special cases, such as getting something comped or at a discount, tip as though you paid full price, particularly if it was for something that wasn't the fault of the restaurant or its personnel.
- On which note, remember that many things are out of your waiter's control. A fight with your boyfriend or a fussy child, yours or someone else's, is probably out of the server's hands.
- If you take up a relatively small percentage of the seats at the table, or are there an unusually long time, tip more. A party of three at a table for four is not obliged to tip a third more, and a person sitting alone at a table for two certainly doesn't need to tip twice as much, but bump it up a little.
- Tipping anyone but the waiter and the coat-check person is optional2 except for a particular favor, but if you feel the need, $1 for the host and 15% of the wine bill for the sommelier are not unreasonable.
If you're at the restaurant where my girlfriend's sister works, the hostess gets $3.
- The coat-check person should get $1 to $2 per coat if it's free, $0 to $1 if it isn't. Many places where coat checking isn't free, it's because people don't tip -- it's essentially tipping made mandatory. Speking of mandatory, if the coat check is mandatory and not free I'd tip nothing.
- Do not tip the waitress with your penis. If you're intellectually capable of reading this, of course, that probably doesn't need to be said.
- At a buffet, where the waiter brings drinks and arranges for you to have the attention of the busing staff, tip 10%.
- This applies to any other restaurant where the waiter does some but not all of relaying your food and drink orders to the kitchen and conveying your food to your table.
- At a bar, I usually leave $1 per drink or 20%, whichever is more.
- If I'm running a tab, it'll be $1 per drink plus $1 unless 20% of the bill comes to more than that.
- At a carry-out restaurant (or "take-away"), I tend not to tip,3 but if it's a counter at which I regularly make an appearance, such as the Starbucks across the street from my office, I will, generally $1 per time for small orders, 10% to 15% for larger ones.
- I've seen it suggested that you should tip more at the take-out counter of a restaurant that also offers sit-down service, but I don't see a reason for that.
- For pizza delivery, I've seen $1 per pie. This seems low to me. I generally tip 25% of the total order, as I do for other deliveries. However, I generally pay 125% of the total cost of the food, including tax—any delivery charge comes off the tip3.
- For other food deliveries, again, 25% of the total, minus delivery fees. If the delivery charge is more than 25% of the total order, tip a dollar or two.
- Hotel room service often includes a delivery charge and a gratuity on top of outrageously inflated prices to begin with, but it can't hurt to slip the guy 10% or so, at least a couple of bucks.
- The valet should get $1 to $5 if the service is free, $0 to $2 if it's not. Remember, you are giving your car keys to this person. However, as with the coat check, if you have to use the valet parking and you have to pay for it, feel free to not tip
- A taxi or limo driver should get about 25%. If there's no charge for using the trunk (or boot), add something anyway if you do use it.
- If you're someplace it's legal for taxis to pick up street hails, and you're going to a neighborhood where these are hard to come by, remember the price of gasoline.
- Skycaps get about $1 per bag. This also applies to shuttle drivers and the like who help you with your bags.
- Hotel porters get about $2 or $3 per bag delivered to or carried from your room and $1 to $2 each for getting them out of storage. If they perform special services, that should be further rewarded. Like with valets, remember these people have access to all your immediately available worldly possessions.
- For room service, see above under "Dining in."
- The doorman gets $1 each time he does something for you, like hails a cab or finds a hooker.
- Leave the maid $1 to $5 (at a really upscale place) per person per night when you check out, more if you've been leaving used condoms in the trash, however well wrapped, or if one of your party got her period all of a sudden4.
- Someone delivering furniture should get $5 or more per item, and that's for going up the elevator and dumping everything in a pile. If there are stairs or setting up involved, tip more.
- The tattoo artist may be an independent contractor who will simply ask for the amount of money he or she expects to receive. However, there are equipent and overhead costs. Tip 10% to 20%, according to the intricacy of the work.
- A piercer should get 10%, more if you're getting a lot done at once.
- A topless dancer or stripper should get $1 to $5 each time she comes around. If she has big tits or less body hair than you expected, tip more. Many work solely for tips.
- Anyplace else where there's a little basket labeled "tips," it can be ignored. If the sign indicates anything more than that tips are to be deposited in that receptacle -- e.g., "tips please!" or "we're poor college students!" or, worst of all, "tipping is customary" when that simply isn't the case -- stifle any impulse you have to leave something, although try to avoid filching a dollar from the basket.
1And auduster strongly urges that you never ever ever do any of this in the U.K.
2That is, even more optional than tipping is generally.
3If you feel this is unfair, feel free to /msg me to explain why. I'll likely change the write-up. I may even change my practice.
4Er, I would imagine.