How to calculate a tip without a calculator

Start with the 10% shortcut

Ten percent is the easiest tip amount to find mentally because you only move the decimal point one place to the left. A $32.50 bill becomes $3.25. A $78 bill becomes $7.80.

Once you know 10%, you can build most common tip percentages from that one number. This is faster and less error-prone than trying to multiply the full bill by a decimal in your head.

How to estimate 15%, 18%, and 20%

For 15%, calculate 10% and then add half of that amount. If 10% of a $60 bill is $6, half is $3, so a 15% tip is $9.

For 20%, simply double the 10% amount. For 18%, start with 20% and subtract 2%. You can estimate 2% as one-fifth of the 10% amount. On a $50 bill, 20% is $10 and 2% is $1, making 18% equal to $9.

• 15%: 10% plus half of 10%
• 18%: 20% minus one-fifth of the 10% amount
• 20%: double the 10% amount

Round first when you need speed

If the bill is $47.63, rounding to $48 makes the calculation easier and changes the tip by only a few cents. For a 20% tip, 20% of $48 is $9.60.

You can also round the final tip to a convenient whole-dollar amount. The goal of mental tip math is a sensible estimate, not a result accurate to the last cent.

Tip before or after tax?

People use both approaches. Tipping on the pretax subtotal is the traditional calculation, while tipping on the final total is simpler and slightly more generous. Check whether a service charge or gratuity is already included before adding another tip.