How to calculate a tip
By Dexaloop · Updated 27 October 2026 · Checked against the sources listed below
To calculate a tip, turn the percentage into a decimal and multiply it by the bill before tax. An 18% tip on a $55.00 meal is 55 × 0.18 = $9.90. That tip, the bill and the tax together make the amount to pay, and a group shares that amount out. Most of the time you do not need a calculator: a few mental shortcuts get you within a cent. This guide covers those shortcuts, why the pre-tax bill is the usual starting point, how to share a tip fairly, and what US and UK guidance says, checked on 27 October 2026.
Turning a percentage into a sum
"Percent" means "out of a hundred", so 18% is 18 hundredths, or 0.18. Multiplying by 0.18 is the same as taking 18 pennies from every dollar. Once you see it that way, the arithmetic has three parts:
- The tip is the pre-tax bill multiplied by the decimal.
- The amount to pay is the bill plus the tax plus the tip.
- A fair share is that amount shared out between the people at the table, equally or by what each ordered.
The one judgment call is the starting figure in part 1, covered next.
Why the pre-tax bill is the usual base
A tip rewards service. Sales tax is not part of the service; it is a charge set by the government and passed on by the restaurant. That is why US etiquette guidance quotes tips on the pre-tax price. The Emily Post Institute, a long-standing etiquette authority, lists sit-down wait service as "15-20%, pre-tax" and buffet service as "10%, pre-tax."
Tipping on the total with tax is more generous, and nobody will object. The difference is always the tip percentage times the tax. On a bill with $3.20 of tax and an 18% tip, the gap is 0.18 × 3.20, or 58 cents. Neither choice is wrong; just know which one you are making.
| Bill before tax | 15% tip | 18% tip | 20% tip |
|---|---|---|---|
| $30.00 | $4.50 | $5.40 | $6.00 |
| $45.00 | $6.75 | $8.10 | $9.00 |
| $55.00 | $8.25 | $9.90 | $11.00 |
| $70.00 | $10.50 | $12.60 | $14.00 |
| $110.00 | $16.50 | $19.80 | $22.00 |
Mental maths shortcuts
Every shortcut starts from one easy figure: one tenth of the bill. Dividing by ten just shifts every digit one column to the right, so a tenth of $55.00 is $5.50. From there you can build any common tip.
- 20%: two tenths. $5.50 + $5.50 = $11.00.
- 15%: one tenth plus a half of one tenth. $5.50 + $2.75 = $8.25.
- 18%: 20% less 2%. One fifth of a tenth is 2%, here $1.10, so $11.00 less $1.10 = $9.90.
- 25%: a quarter of the bill. $55.00 ÷ 4 = $13.75.
- Any percentage: count 1% (the bill with the digits shifted two columns, here $0.55) and multiply. 17% is 17 × $0.55 = $9.35.
A sense check helps catch slips. A tip between 15% and 20% should be a little under a fifth of the bill. If your answer is more than the bill or only a few cents, the decimal point has moved the wrong way.
Worked example: three colleagues at lunch
The receipt shows a $55.00 subtotal and $3.20 tax. The three agree on 18% before tax.
- Tip: 55.00 × 0.18 = $9.90.
- Amount to pay: 55.00 + 3.20 + 9.90 = $68.10.
- Equal shares: 68.10 ÷ 3 = $22.70 each.
That one comes out exactly. Many bills do not. If the amount were $68.11, a third would be $22.7033..., and since no one can pay a fraction of a cent, two people pay $22.70 and one pays $22.71. Always check that the shares add back to the amount on the receipt.
Paying in cash? Rounding each share up to $23.00 collects $69.00, which is $0.90 more. If that goes to the server, the tip becomes $10.80, which is about 19.6% of the pre-tax bill. Rounding up is an easy way to be generous; just agree as a group that the extra is part of the tip.
Sharing fairly when orders differ
An equal split is fair only when everyone ordered about the same. If one person had a salad and another the most expensive main, share in proportion instead:
- Total each person's own items before tax.
- Give each person a slice of the tax in the same proportion: their items ÷ the subtotal × the tax.
- Apply the agreed tip percentage to each person's own items.
In the lunch above, suppose Priya's dishes came to $30.00. Her slice of tax is 30 ÷ 55 × 3.20 = $1.75, and her 18% tip is $5.40. She pays 30.00 + 1.75 + 5.40 = $37.15. The other two share the remaining $30.95 the same way, based on their own dishes.
What the guidance says
United States
Beyond restaurants and buffets, the Emily Post Institute's guide says take-out carries "No obligation," with 10% suggested for extra service such as curbside delivery or a large, complicated order. These are etiquette suggestions, not law, and local custom varies.
United Kingdom
UK government guidance is about where tips end up, not how much to leave. It states: "By law, all tips must be given to workers without deductions." It also explains service charges, which the business adds to the bill: "If the charge is compulsory, it’s not a tip." So if a UK bill already shows a service charge, read it carefully before adding anything more.
Elsewhere
Customs vary widely. In some countries a service charge is standard and extra tipping is unusual; in others tipping is rare. Check a reliable local source before you travel.
Common mistakes
- Tipping twice. Look for "service charge" or "gratuity included" on the bill first.
- Tipping on a discounted price by accident. A voucher lowers the price, not the work. Decide on purpose which figure to use.
- Misplacing the decimal. 15% is 0.15, not 1.5.
- Rounding shares down. That leaves the table short. Round up, or hand out the leftover cents one at a time.
- Splitting evenly when orders differ a lot. Use proportional shares so nobody pays for someone else's meal.
The calculator below lets you choose whether the tip is on the bill before or after tax, splits the amount between any number of people, and can round each share up.
Work out a tip and split it: tools.dexaloop.com/tip-calculator/. Free, no sign-up, and it runs on your device.
Questions
How much extra is it to tip on the total with tax?
The tip percentage times the tax. With $3.20 of tax and an 18% tip, tipping on the total adds 0.18 x 3.20 = $0.58. On most bills the difference is small.
How do I work out 18% in my head?
Find 20% and take away 2%. On a $55 bill, 20% is $11.00 and 2% is $1.10, so 18% is $9.90.
Should I tip on the price before a voucher or discount?
That is your choice, but the service was the same either way. Many people tip on the full price; if you tip on the reduced price, do it on purpose rather than by accident.
Is a UK service charge the same as a tip?
Not always. GOV.UK says that if a service charge is compulsory, it is not a tip. Read the bill to see whether a charge was added before deciding whether to leave anything more.
What is a fair way to share a tip when people ordered different amounts?
Give each person the same tip percentage on their own items. Someone whose dishes came to $30 pays a $5.40 tip at 18%, while someone whose dishes came to $12 pays $2.16.
Sources
- The Emily Post Institute: General tipping guide
- GOV.UK: Tips at work
- GOV.UK: Tips at work, Tips and tax (service charges)
This guide is general information, not legal, tax or financial advice. Rules change; check the official source for your own case. Found a mistake? Email support@dexaloop.com.