The basic formula
Tip = bill × (tip percentage ÷ 100)
First decide which bill amount you want to tip on. Convert the percentage to a decimal, then multiply. The result is the dollar tip.
Worked example
- Start with a $64 pre-tax bill.
- Choose 20%: 20 ÷ 100 = 0.20.
- Multiply $64 × 0.20 = $12.80.
- Without tax, the total is $76.80. Add any applicable sales tax separately.
Quick mental math: 10% of $64 is $6.40, so 20% is twice that: $12.80.
Common mistakes
Do not calculate the tip percentage from the amount after tip, unless that is intentional. If your receipt already includes gratuity, review it before adding another tip.