If service is poor, consider whether it's the server's fault. Reduce the tip or leave the minimum, says Peggy Post, director of The Emily Post Institute.

• If the wait staff has been surly or truly hasn't done a good job, talk to the management to give them a chance to make things right.

• Many restaurants add an 18 percent to 20 percent gratuity for parties of six or more. Why? Large parties can get distracted and forget the tip, explained Robert Damante, general manager at RACKS Downtown Eatery +Tavern in Boca Raton.

• In some resort areas, tips are included in the bill, regardless of the diner count. To avoid double-tipping, check your bill, Post said.

• Who tips best? Guests who pay with credit cards, drinkers, and late diners, who tend to leave about 5 percent more than average, said Michael J. Mellion, co-owner of Havana's Cuban Cuisine in Cooper City.

Should tips be calculated before or after the tax?

• To help guests calculate gratuity, the credit card receipts at Havana's Cuban Cuisine in Cooper City have 15 percent, 20 percent and 25 percent suggested tip amounts printed at the bottom.

Restaurant experts say it's a common practice. While some diners bristle at the thought of tipping on the after-tax bill, others shrug it off as a small difference, or say they don't mind because servers generally are underpaid.

Peggy Post says it's proper protoccol to subtract the tax before calculating the tip. EtiquetteScholar.com calls 15 percent on pre-tax total the minimum tipping standard for service in restaurants nationwide.

Still Post said most people don't bother to subtract the tax before figuring gratuity. Tipping is a way of saying thanks for the service, and that's what diners should keep in mind when deciding gratuity, Post said.