Tipping customs vary by country, but in the United States 15 to 20 percent is the standard range for restaurant table service, with 18 percent a common default and 20 percent the norm for excellent service. Many servers earn a below-minimum cash wage with tips expected to make up the difference, so the tip is genuinely part of their pay, not a bonus. The math is simple — bill times the rate — but splitting the total evenly across a table, adjusting for tax, or handling large-party auto-gratuities is where a calculator earns its keep. Outside the US, check local norms: in Japan tipping can offend, while in much of Europe a small rounding-up suffices because service is included.
Two points of etiquette matter for the numbers. First, tip on the pre-tax subtotal, not the total with tax — tipping on tax means tipping the government, not your server, and on a big bill the difference is real money. Second, when splitting, divide the grand total (bill + tip) by the number of diners rather than having everyone guess their share; rounding each share up to the nearest dollar keeps things clean and lands slightly generous, which is the right direction to err. For delivery, 10 to 15 percent or a few dollars minimum is typical, more in bad weather; for bars, $1-2 per drink is the convention. Large parties often trigger automatic gratuity — typically 18 percent for groups of 6 or 8+ — printed right on the menu. That auto-gratuity is legally a service charge, not a tip, which matters because it is not yours to adjust downward for slow service (take it up with the manager instead). When the auto-gratuity is 18 percent and service was great, adding a few percent extra on top is a classy move that servers remember. And on business meals, the full bill including tip is usually reimbursable — keep the itemized receipt, not just the card slip.