Only half of restaurant tippers fall within the gratuity sweet spot of 16 to 20 percent, according to a new report by CreditCards.com.
The study, a survey conducted last month, examined tipping behavior at restaurants, hotels, coffee shops and hair salons. It sampled 1,002 adults who used cash, credit or debit cards.
It found that the most generous tippers in the U.S. are Republican men who live in the Northeast and use a credit or debit card. They generally tip at a median of 20 percent when dining at a sit-down restaurant.
On the other hand, it said, women tip a median of 16 percent, while Democrats, Southerners and cash users tip a median of 15 percent.
"People now see 15 percent as a floor rather than a ceiling when it comes to tipping. The truth is that the median was about 18 percent. So, it's somewhere between 15 and 20," Matt Schulz, senior industry analyst at CreditCards.com, said Monday on CNBC's "Squawk Box."
"It's really all about income," Schulz said. "The more cash you have, the more likely you are to plunk a little more down at the table at the end of the night."
The survey found that 27 percent of hotel customers always tip their housekeeper, 29 percent who visit coffee shops always tip, and 67 percent always tip their hair stylist and barber.
Men tend to be more generous restaurant tippers than women, but women are better when it comes to hotel housekeeping, baristas and hair stylists.
"My general rule of thumb is if it is a business you are going to go to and you're going to spend time there, and a person you're going to see on a regular basis, when in doubt give a tip," Schulz said.