Enter the bill, choose a tip percentage, and set how many people are paying. The calculator shows the tip, the total and the amount each person owes, and can round the per-person figure to a sensible number so nobody is counting out small change.
Tipping on the pre-tax subtotal is the common convention in the United States, though many people simply tip on the full total for speed. On a typical bill the difference is small; this calculator tips on whatever figure you enter.
In the United States, 15-20% is standard for table service. In much of Europe service is included and rounding up is enough. In Japan tipping is generally not expected. Local convention matters more than any single number.