“I would much prefer everybody get a raise and do it the way the Europeans do and include it in the price,” said Helaine Olen, a personal finance blogger and author of the book “Pound Foolish: Exploring the Dark Side of the Personal Finance Industry.” “But we don’t live that way.”

Instead, Ms. Olen said, people should plan for tipping obligations like other household expenditures. “You need to just sort of budget it in the same way as if you’re going to fly and you know the airline is going to charge for your suitcase.”

Image DipJar makes it easy to tip with a credit card at Dos Toros Taqueria in New York. Credit... Nicole Bengiveno/The New York Times

Tipping as an American practice stretches back centuries. “There are records of George Washington and Thomas Jefferson giving tips to their slaves,” said Michael Lynn, a professor of consumer behavior at Cornell University’s School of Hotel Administration, who has studied changes in tipping habits. In the 1940s, he said, the average restaurant tip was about 10 percent. “It’s very clear that tip sizes have increased over time,” he said, adding that he could not predict how high they would go.

Some question whether expected tips will edge up to a point where they can no longer be counted on as “add-ons,” leading employers to rethink pricing and salary structures. Patrons of the fast-growing car service Uber frequently cite its ban on tips as one of the attractions, even if prices are higher than for taxi fares. A brew pub called Public Option that is scheduled to open in Washington, D.C., will not allow tipping; its owner has said he plans to pay his workers at least $15 an hour.

Still, the concept of tipping is spreading. In March, a Silicon Valley company opened ChangeTip, a platform that allows people to send small Bitcoin payments through social media, email, Skype or text to show their appreciation for content creators (or anyone) on the Internet.

The service has been growing about 30 percent a month and now has about 60,000 users who have collectively tipped over $250,000, said Nick Sullivan, founder and chief executive. The average payment, he said, was a little over $1.