To use the tip calculator, either speak or type, “What is the tip for $30,” “How much is the tip for $40,” or even, “How much should I tip for $50.” Google will default the tip to 15%, but this is easily adjustable up or down depending on the level of service you have received.
You can also split the bill between several different people, and Google will tell you how much each person should tip, along with the total of how much each person should pay.
I’m not sure how long this feature has been included in Google Search and Google Now, but it’s fantastic and incredibly useful. Now I just have to resist the urge to eat out and use this, when I’ve got perfectly good leftovers waiting for me in the fridge…