Work out the tip and split the bill in seconds.
A tip is a percentage of the bill for service, and how much is customary varies a lot by country. In the United States, 15–20% is standard for table service and effectively expected; across much of Europe a service charge is often included and a small round-up is enough; in some countries tipping is not customary at all. The calculator above works out the tip and the total, and splits it between any number of people.
Splitting fairly. To split evenly, divide the grand total (bill plus tip) by the number of people. If shares are uneven, it is fairer to tip proportionally to what each person ordered rather than splitting the tip equally on top of unequal meals. For large groups, check the bill, as many restaurants add an automatic service charge, in which case an extra tip is optional.
Tip on pre-tax or post-tax. Convention is to tip on the pre-tax amount, though many people simply use the total for ease. Either is fine; the difference is small. What matters more is tipping consistently for good service and adjusting for exceptional or poor experiences.