Most etiquette guides recommend tipping on the pre-tax subtotal, since tax isn't part of the service you're tipping for. In practice many people just tip on the total for simplicity — this calculator lets you choose either way.
Sit-down restaurants: commonly 18–20% for good service, 15% for adequate service, 25%+ for exceptional service. Bars: $1–2 per drink or ~15–20%. Delivery: 10–20% with a minimum of a few dollars. Buffets and counter service are more variable — tip what feels right.
Enter what each person spent before tax. Tax and tip are then divided in proportion to each person's share of the subtotal — so someone who ordered a $40 steak pays more of the tip than someone who ordered a $12 salad, which is fairer than splitting everything evenly.