Tipping is a customary practice in many countries, particularly in the United States, where service workers often depend on gratuities as a significant portion of their income. The standard tip at a sit-down restaurant typically ranges from 15% to 20% of the pre-tax bill, with 25% or more reserved for outstanding service.

The formula is simple: Tip Amount = Bill Amount x (Tip Percentage / 100). When splitting the bill, divide the total (bill plus tip) evenly among the group. Some people prefer to calculate tips on the pre-tax subtotal, while others tip on the full after-tax amount. Either approach is acceptable.

For example, an $85 bill with an 18% tip yields a $15.30 tip and a $100.30 total. Split between two people, that is $50.15 per person ($42.50 for food plus $7.65 for tip). Quick mental math tricks include calculating 10% by moving the decimal point, then adjusting: 20% is double the 10% amount, and 15% is the 10% amount plus half of it.