Calculating a tip is simple once you reduce it to a percentage of the bill. For 20%, move the decimal point one place to find 10%, then double it. On a $64 check, 10% is $6.40, so 20% is $12.80.
Fast mental shortcuts
For 15%, find 10% and then add half of that amount. For 18%, a calculator is often faster: multiply the bill by 0.18. For 25%, divide the bill by four.
Splitting a restaurant bill
First decide whether you are tipping on a shared subtotal or on each person's individual items. Add the tip, then divide the final total by the number of people only if everyone agreed to an even split.
Tax and tipping
People use different conventions about whether the percentage is based on the pre-tax or after-tax total. Follow your own preference and local norms; the important part mathematically is knowing which number you are using as the base.
Use the calculator
Open the free Tip Calculator to enter any bill, percentage, and group size.