If you tend to experience difficulty in determining the exact amount you should tip for a service, try the 'What Should I Tip?' app.
First of all, you can program the app to be in line with your own personal tipping philosophy, so you can be fair, generous or stingy according to your preferences. Input how much the bill was and rate the quality of the service using four easy choices. The app will calculate how much tip you should leave, and if you are still confused, it will tell you how much your total bill with tip should add up to.
This tip calculator app also helps you break the bill evenly among friends and works with international currencies as well.