How to calculate a tip on $100
Calculating a tip on a $100 bill is straightforward: multiply the bill by the tip percentage expressed as a decimal. For a 20% tip that is $100 × 0.20 = $20.00, bringing your total to $120.00.
In the US, the standard tipping range for sit-down restaurants is 18–20% for good service, with 15% considered adequate and 25% reserved for exceptional service. Servers typically rely on tips as the primary source of their income — the federal tipped minimum wage is just $2.13 per hour.
If you are splitting a $100 bill with a group, the cleanest approach is to divide the full total (including tip) equally. The table above shows per-person amounts for 2, 3, and 4 diners at each common tip percentage.
A quick mental math trick for 20%: find 10% of your bill by moving the decimal one place left ($100 → $10), then double it ($20). For 15%, add half of the 10% figure to the 10% itself.