For starters, here's a simple rule for restaurant tipping: Leave 15 to 20 percent of the pretax total of your bill. Don't dip below 15 percent unless the service has been abysmal—and never skip a tip. (If a server has been rude or offensive, speak to the manager.)
Because 20 percent is what most people leave, you might want to aim for that. It's easy to calculate in places (Washington, D.C., for example) where the tax is 10 percent. Just double the tax and round up. (If tax on a $47 tab is $4.70, your tip should be $10). Otherwise, simply divide the total by 10 ($47 divided by 10 equals $4.70—move the decimal point one place to the left), double that, and round up.
If you're truly math-challenged, the calculator on your smartphone should do the trick: Simply multiply the pretax total by 0.15 or 0.2 and voilà, your tip appears.
And contrary to what you may have heard, alcohol should be tipped at the same rate as food, unless you're knocking back $1,000 bottles, in which case you could figure 10 percent on those. But as a general rule, tip on the total cost of the meal, drinks included.
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Where things get dicey is a group dinner at which everyone eats and drinks differently. Spare yourself the tedious "So I just had the mushroom appetizer and tap water, and Bill had two martinis and the prime rib . . ." conversations that always end with someone feeling put out. The apps at right let you split the tab and tip with ease and accuracy by allowing you to assign certain dinner-tab items to certain diners, or keep track of who owes what. But read the privacy and terms-of-use disclosures before using these tools to make sure you're comfortable with the kind and amount of information they collect.
Tab: free, for Android and iOS.
Settle Up: $1.99, for Android and iOS. (It works with foreign currencies, so it's a good choice for international travel.)
Plates by Splitwise: free, for iOS.
Your One-Stop-Shopping Tip Guide
We asked etiquette experts—Diane Gottsman, author of "Modern Etiquette for a Better Life" (Page Street Publishing, 2017), and consultant Julia Esteve Boyd—to recommend which service providers to tip, and the amount. These suggested tips represent their combined recommendation.
Server
Hairdresser
Pedicurist
Editor's Note: This article also appeared in the February 2019 issue of Consumer Reports magazine.