According to a new study from creditcards.com, 10% of millennials do not tip at all when eating out. In contrast, only 3% of the older generations don’t tip.

Even when millennials do tip, the study found that the median gratuity is just 15%. This is under the national average, and significantly less than Gen-X, baby boomers, and the ‘Silent Generation,’ all of whom leave a median tip of between 18 and 20%.

The same attitude applies to tipping those who provide services, such as Uber or Lyft drivers: 18% of millennials don’t tip them, even when provided with an option to do so. Nevertheless, close to 27% of the millennials surveyed suggested that they would prefer having a service charge included in items, thereby paying higher prices, and then doing away with tips.

But it’s not just millennials who are unlikely fork over more than 15%. Parents with young children, lower wage earners, and the less educated tip less than the overall median of 18%.

So who are the most generous?

Older people are among the most generous, with close to 55% of those over 65 tipping 20% or more. Women also tend to leave bigger tips than men, a median of 20% compared to 16%. Those who are college-educated or hail from the Northeast or Midwest also tend to leave a median of a 20% tip—above the national average.