Tipping and splitting a bill
A tip is a percentage of the bill, so the arithmetic never changes: tip = bill × (percentage ÷ 100), and the total is the bill plus that tip. What varies is the percentage people use and how the total gets divided. This calculator handles both at once — enter the bill, pick a tip rate from the chips or type your own, and say how many people are splitting it.
Splitting evenly, and rounding for cash
Dividing the total by the number of people gives an exact share that rarely lands on a round figure. The round-up option pushes each share to the next whole unit of currency, which makes cash payments painless — nobody is counting out small change — and quietly increases the tip. The calculator reports how much extra that adds and what the tip percentage has effectively become, so you can decide whether it is still reasonable.
Customs differ by country
Tipping norms are cultural, not mathematical. In some countries a service charge is already printed on the bill and an additional tip is optional; in others staff are paid a lower base wage on the assumption that tips will make up the difference; in others again, tipping is simply not part of the culture. Before travelling, it is worth checking what is normal where you are going — and checking the bill for an existing service charge so you don't pay twice.