Hot tip for millennials: Tip your waitstaff.

Millennials are cheapskates compared to other generations, a new CreditCards.com report suggests: One in 10 say they usually don’t leave any tip for restaurant servers, versus 3% of people from older generations. And nearly one in five millennials (18%) tend not to leave any money in transactions involving pre-inputted tip amounts, e.g., in cabs and ride-hailing services, coffee shops and food trucks — compared with 12% of older folks.

“In some ways, it’s not surprising at all because of the well-documented financial struggles of millennials — whether it’s struggling to get their feet under them career-wise, or student loan debt, or any of myriad other reasons,” Matt Schulz, senior industry analyst at CreditCards.com, told Moneyish. “On the flip side, the typical restaurant worker is a millennial. So in some ways, it seems a bit self-defeating.”

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Millennials — defined in the report as people aged 18 to 37, versus Pew Research’s age range of 22 to 37 — also tipped a median 15% at restaurants, in contrast to the overall 18% median. Meanwhile, 51% of people aged 38 and over said they tipped at least the standard 20% at restaurants, while only 36% of millennials said the same. “It’s across the board,” Schulz said.

Whatever the reason for their stinginess, he added, “it’s clear that millennials are lagging behind older generations when it comes to tipping.” “If somebody ends up cursing you out or spilling soup all over you, it’s one thing if you don’t tip,” he said. “But beyond that, you need to tip — because these folks’ livelihoods depend on it.”

Other below-average tippers included men, Southerners, people from the Western U.S., parents with young kids, less-educated people and low earners, according to the survey. “Quite a few of those might simply get down to a question of income,” Schulz said, “where these folks have less financial margin for error in their day-to-day lives and thus can’t afford to be as generous with tipping as other folks are, or as they themselves might like to be.”

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One silver lining: 42% of respondents overall said they tended to tip 20%. “The days of 15% being the standard tip amount, I think, are in the past,” Schulz said. “We see lots of indications of people edging up closer to 20%, and that’s good news for folks in the service industry.” Meanwhile, 23% said they usually opted for 15%, 17% gave less than that, and 6% said they left typically left no tip.

The study included responses from 1,000 adults gathered between May 18 and May 20.

The Emily Post Institute prescribes a 15 to 20% pre-tax tip for sit-down wait service at a restaurant, and 10% pre-tax for wait service at a buffet. While there’s no obligation to tip on takeout, the Institute says, you should offer 10% for a large, complicated order or for extra service like curb delivery. As for home delivery, go with 10 to 15%, or $2 to $5 for pizza “depending on the size of the order and difficulty of delivery.” Bartenders should get a 15 to 20% tip on your tab, or one to two dollars per drink.

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Millennials are more likely than older generations to eat out, according to a 2017 Bankrate study: They dine at restaurants or order takeout nearly five times a week, versus Gen Xers’ average of 3.4 times a week and Boomers’ 2.5 times.

While tipping can be an awkward situation to navigate, Schulz said, “be generous” when in doubt. “It may just be etiquette to you,” he said, “but it’s food on somebody else’s table.”

Millennials have at least shown generosity in other ways. For example, 84% of them made a charitable donation in 2014, according to the 2015 Millennial Impact Report survey of more than 2,500 millennial employees and managers. While 22% of those givers said the donation was solicited through their company, the other 78% gave on their own. And seven in 10 millennial employees spent at least an hour volunteering in 2014.