Choose a tipping basis before doing the math

Tipping customs and bill layouts vary by place and service. First decide what amount you intend to tip on—before or after tax, before or after a discount—and whether a service charge or gratuity has already been included.

Then calculate the percentage from that chosen base, round as you prefer, and check the final total. A tip calculator can handle the arithmetic, but it cannot decide the local custom or whether an included charge goes to staff. Read the receipt carefully before adding another tip.

For a group, agree on the method before splitting the bill.