How to calculate a tip
Tip = bill × percentage ÷ 100. In your head: move the decimal one place left for 10%, then double it for 20% or add half for 15%.
The 10% trick, step by step
Every common tip is a simple multiple of 10%, and 10% is the easiest percentage there is: shift the decimal point one place to the left. Pick a bill, choose the tip you want, and step through it.
Why does this work? Percent means "per hundred", so 10% is one tenth, and dividing by ten in our base-ten number system just slides every digit one place over. 20% is two tenths, 15% is one and a half tenths, 25% is a quarter. Once you see tips as "tenths of the bill", the arithmetic stops being scary. That same click of understanding is what ahaboo aims for, with hands-on explainers you can drag and zoom through, including one on US tax brackets.
The formula
Tip = pre-tax bill × tip % ÷ 100, and total = bill (with tax) + tip. For an 18% tip on a $64.20 subtotal with $5.70 tax: tip = 64.20 × 0.18 = $11.56, total = $69.90 + $11.56 = $81.46.
To split it, divide the total by the number of people: $81.46 ÷ 3 = $27.153…, so two people pay $27.15 and one pays $27.16. The tip calculator does this for you, cents included.
Shortcuts for each percentage
| Tip | Mental shortcut | On $50 |
|---|---|---|
| 10% | Move the decimal one place left | $5.00 |
| 15% | 10% plus half of it | $7.50 |
| 18% | 20% minus a fifth of 10% | $9.00 |
| 20% | 10% doubled | $10.00 |
| 22% | 20% plus a fifth of 10% | $11.00 |
| 25% | Divide the bill by 4 | $12.50 |
Common mistakes
- Tipping on tax. Not wrong, just a bit more than the percentage you meant. See the tip screen guide for how card machines do it.
- Tipping on the discounted price. With a coupon or gift card, tip on the original amount.
- Tipping twice. If "gratuity" or "service charge" is already on the bill, you've tipped. The gratuity calculator shows what it came to.
Want to check without doing any math? The tip chart lists 10–25% for bills from $5 to $500.
Questions people ask
What is the formula for calculating a tip?
Tip = bill × tip percentage ÷ 100. For an 18% tip on $55: 55 × 18 ÷ 100 = $9.90. Total = bill + tip.
How do I calculate 15% of a bill quickly?
Take 10% (move the decimal one place left), then add half of that. On $42: 10% is $4.20, half is $2.10, so 15% is $6.30.
How do I calculate 20% of a bill quickly?
Take 10% and double it. On $73.50: 10% is $7.35, so 20% is $14.70.
How do I work out what percentage I tipped?
Divide the tip by the pre-tax bill and multiply by 100. A $12 tip on a $60 bill is 12 ÷ 60 × 100 = 20%.
Is there a trick using the tax on the receipt?
In places where sales tax is close to 10%, doubling the tax gives roughly a 20% tip. It only works where the tax rate is near 10%; at 6% tax, doubling gives only 12%.