When it comes to tipping, millennials are the worst. That's the conclusion of a survey released Monday, which found young adults to be far less generous than older generations when it comes to rewarding their servers at restaurants.

Ten percent of Americans aged 18 to 37 said they routinely leave no gratuity for restaurant servers, while almost one in three said they typically leave less than 15 percent, according to the CreditCard.com findings.

Americans 65 and old are better bets for those who rely on tips to earn a living, with almost 55 percent of senior citizens saying they tip 20 percent or more at restaurants. Just 35 percent of folks under 30 said they were equally generous.

When given an array of tipping options, such as one might find at a coffee shop, food truck or in a taxi or ride-hailing service, about one in six millennials said they regularly pick the lowest figure, and nearly one in five select no tip.

Young adults on average make less than those further along in their careers, but income alone is unlikely to be the sole factor behind the findings, based on an online survey of 1,000 adults during a three-day period in May. 

Younger Americans are more likely to be supportive of getting rid of the practice of tipping altogether, an approach that is being tried at some restaurants, but is by no means a major trend.

Tipping, a practice treated as standard in the U.S. but not so much in other countries, is increasingly being questioned, given research that shows a server's age and appearance has much to do with how much one earns in tips.

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