A new poll shows that when it comes to tipping, many Americans are shortchanging their servers.

The Pew Research Center poll of 12,000 people, which came out on Thursday, shows that 57 percent of American diners tip 15% or less for a typical sit-down meal, "including 2% who say they wouldn’t leave any tip," Pew researchers wrote.

Only about 22 percent of people said they would leave a tip of 20% or more," Pew found.

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What factors into how Americans are tipping?

The amount that people tip varies depending on their age, income, and other factors, the poll found.

Younger adults are slightly more likely to be more generous with their tips than their older counterparts, who tend to be more conservative with their wallets, the poll found.

For some, the location makes a big difference. At fast-casual restaurants like Chipotle and Sweetgreen, or quick stops at coffee shops, only about 25% of Americans say they will usually or frequently tip, according to Pew.

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Americans are upset growing expectations to leave tips

Among concerns of those surveyed was frustration over expectations to leave tips in increasingly more situations outside of restaurants.

According to Pew, 72% of people said that tipping is now expected in more places than five years ago. Only about a third of respondents said they find it easy to determine when and how much to tip for different types of services, like food deliveries and pet sitters.

In hopes of taking out some of the guesswork and ensuring their staff get adequate tips, many bars and nightclubs now include gratuity in the bill, typically ranging from 18 to 25%.

"I'll look at the bill and see a 20 percent gratuity charge," Lawrence Edgerton of New York City told USA TODAY about some of his experiences getting drinks with co-workers.

"Like, how they even know I like the service?" said Edgerton, a membership coordinator at a private club. "In cases like this I don't add an extra tip."

Kaia Grey, a 24-year-old flight attendant in Washington, D.C., says it seems like service fees are the norm at bars, restaurants and lounges in the country's capital.

"I literally can't go anywhere in D.C., and it will be a service fee," she said. "I have to be mindful when ordering because the more I order, the higher the surprise fee is."

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When to tip?

It's a common practice for most Americans to leave a gratuity when dining at a restaurant, but there seems to be some uncertainty around tipping in other situations. Many people are unclear about when and how much to tip in situations such as hotel stays, haircuts, or rideshares.

“Even as Americans say they’re being asked to tip more often, relatively few have a great deal of confidence about when and how to do so,” Pew researchers said.