Find the bill total before tax or after tax, depending on your preference
Choose a tip percentage, such as 15%, 18%, or 20%
Convert the percentage to a decimal
Multiply the bill total by the decimal
Round to a convenient amount if needed
Add the tip to the bill total to get the final amount
For a quick estimate, move the decimal one place left for 10% and double it for 20%
For 15%, find 10% and add half of that amount
For 18%, find 10% and add 8%
For 20%, double the 10% amount