Are you tipping your Uber driver enough?

This week, Uber launched an option for riders to tip within its app. For now, it is only available in Seattle, Minneapolis, and Houston, but Uber plans to roll it out to every U.S. city by the end of July 2017.

No doubt, many riders will welcome this option, but they’ll also be wondering how much — if anything — they should be tipping their driver. (For its part, Uber says that while “it does not require riders to offer drivers a cash tip, you are welcome to do so.) So Moneyish asked tipping experts to weigh in.

“These drivers are basically fulfilling the role of taxi driver as far as tipping norms are concerned, so add gratuity as though you’re in a yellow cab,” explains Inc’s Tess Townsend.

Tips should be a percentage of the fare, like you’d tip in a taxi — 15-20%, or if you’re only going a short distance $2 – $5, Pam Eyring, president of The Protocol School of Washington, tells Moneyish. She says you should tip if the driver picked you up quickly and gets you to your destination efficiently, is courteous and has a clean car. She adds that tipping is also appropriate if you’re heading to or from the airport, and they load your luggage into the car or if you ask them to make a quick stop along the route.

Eyring says it’s appropriate to skip the tip if the car smells bad, the driver keeps getting lost or doesn’t arrive at your location as expected and you have to contact them. She also adds that you can decline to tip if they “make small talk on topics you shouldn’t talk about such as religion, politics, sex, etc., making you uncomfortable” or if they “try to guilt you into tipping.”