The formula
tip = bill × percentage ÷ 100 · each = (bill + tip) ÷ people
Where it comes from
The tip is a percentage of the bill, and the total splits evenly between however many of you there are. The only real question is what the bill is: whether you tip on the amount before or after tax changes the answer, and both conventions exist.
How to work it out by hand
- Multiply the bill by the tip percentage and divide by 100
- Add that to the bill for the total
- Divide the total by the number of people
- For a quick check, 10% is the bill with the decimal point moved one place left
What is worth knowing
Customs differ enormously and the percentage is the smaller part of it. In the United States 15 to 20% is expected in restaurants and staff wages assume it. In much of Europe service is included and rounding up is enough. In Japan tipping can cause genuine offence. The mental shortcut worth knowing: take 10% by moving the decimal point, halve it for 5%, and add them for 15%. Everything else is built from those two. If you are splitting unevenly rather than down the middle, this is the wrong tool — work out each share of the bill first, then apply the same percentage to each.