Guilt is a terrible thing to live with, so Starbucks will release an updated iPhone app next week, enabling customers to use their smartphone to leave a tip.

The tipping function is part of Starbuck's upgraded iOS app that rolls out on March 19. The app already allows customers to access their rewards program and to pay for their order at the chain's 7,000 locations. Those wishing to give a little extra will be given the option of leaving a $.50, $1 or $2 tip. Adding digital tipping was one of the most often received suggestions the coffee house chain has received.

"As more and more customers are using their phone to pay, they have also asked for a convenient and meaningful way to show their appreciation to store partners," said Cliff Burrows, group president, U.S., Americas and Teavana. 

Those using Android phones will either have to keep a few extra bucks in their pockets or live with the guilt of not being able to tip, as the company does not plan to roll out this update for its Android app until later this year. Both apps are only for customers in the U.S., UK and Canada.

Digital payment is catching on at Starbucks. The company reported that each week about 11 percent of Starbuck's customers use their smartphone to pay for an order. Overall, about 10 million people are using the mobile app.

"This update to the Starbucks App for iPhone is an important next step in digital innovation at Starbucks and one of the many ways we'll expand and improve our digital experience in the months to come," said Adam Brotman, chief digital officer for Starbucks.

The app received other improvements to make digital payments easier. The customer can now just shake their phone to quickly bring up the rewards card barcode and pay for their order. The user interface was also streamlined and made more accessible.

The card's other features remain unchanged. They can still pay, check their rewards history, look for promotions, reload their Starbuck's Card, find stores and send virtual gift cards to friends.