How much should you give that cute waiter? And when shouldn't you leave a gratuity? As our society becomes more service-oriented, there are more people to tip. And even for the same old services, the protocol can change. Tips for restaurant servers, for instance, have grown over the years. So what's proper now? A rough guide:

Restaurants
Normally, 15 to 20 percent of the total bill—20 percent for a first-class place. Note that people tip more in urban areas. According to the Zagat Survey, the average gratuity in city restaurants across the United States is about 18 percent. If you've had a drink at the bar, leave the bartender 15 to 20 percent, or at least \$1 a drink. Give the coat-checker \$1 a coat. Tipping sommeliers is optional (they usually get a share of the waiters' take), but if you'd like to tip them separately, you can slip them 10 to 20 percent of the cost of wine, in cash. (Subtract that amount from your total tip.) For food that's delivered to your home, tack on 15 percent. What about those tip jars on the counters at coffee and takeout joints? "The level of service a counter employee provides doesn't require a tip," says Peggy Post, head of the Emily Post Institute.

Salons
If the owner cuts your hair, you're off the hook, right? Wrong. Turns out most salon owners welcome gratuities. "Not tipping the owner is an old tradition that's dying out," Post says. She recommends 15 to 20 percent of the fee, whether or not the stylist owns the place. When more than one person (stylist, colorist, blower) attends to you, split 15 to 20 percent among them according to how much each contributed to the outcome. A basic shampoo and conditioning rates \$1 to \$3; a wash involving foil removal and color rinses requires a bit more. Slip 15 to 20 percent each to a masseuse and a manicurist.

Hotels
If it seems as if you have to shell out tips left and right, that's because you do. Figure 15 to 20 percent for the taxi or limo driver, \$1 a bag for the bellhop, and \$1 for the doorman who hails your cab or fetches your car. Room-service deliveries rate 15 to 20 percent of the bill, and the housekeeper gets \$2 a day. As for the concierge, "You might tip \$5 for a dinner reservation, \$20 for theater tickets," suggests Sara-ann Kasner, president of the National Concierge Association. "But if someone goes the extra mile—getting you into a popular restaurant at the last minute or obtaining hard-to-get theater tickets—you can tip upwards of \$25."

Newspaper carrier: \$5 to \$15.
Mail carrier: Postal workers can accept gifts worth up to \$20.
Housekeeper: A week's salary.
Garbage collectors: \$10 to \$20 each.
Doorman: \$25 to \$100.
Super: \$30 to \$100.
Elevator operator: \$20 to \$50.
Personal trainer: Price of one session.
Parking-garage attendant: One third of monthly bill.
Dog walker: A week's salary.
Hairdresser: \$25 to \$100.
Manicurist: \$10 to \$50.

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