Common tip percentages
15% is generally considered the minimum for acceptable sit-down restaurant service in the US, 18-20% is standard for good service, and 20-25% is customary for exceptional service. These norms vary meaningfully by region and by type of service — delivery drivers, bartenders, and salon services often follow different conventions than a full-service restaurant.
Pre-tax or post-tax?
Most etiquette guides recommend tipping on the pre-tax subtotal, not the total after sales tax is added — tax isn't part of what the server or service provider earns, so tipping on it doesn't actually benefit them and just inflates the bill unnecessarily. That said, plenty of people simply tip on the final total out of convenience, and both are common in practice. Enter whichever amount you intend to base the tip on.