How to Calculate a Tip: 15%, 18% and 20% in Your Head
Tipping is the percentage calculation most people do most often, usually under time pressure with a card machine in front of them. The good news: you never need to reach for a calculator. Every common tip rate can be built from one easy number — 10% of the bill.
Find 10% by moving the decimal one place left, then build from it. On a $64 bill, 10% = $6.40. A 20% tip is double that ($12.80), 15% is 10% plus half of it ($9.60), and 18% is 20% minus a fifth of 10% ($11.52).
The 10% anchor method
Ten percent of any number is that number with the decimal point moved one place to the left. $47.80 becomes $4.78. $135 becomes $13.50. That is the whole trick — every other tip rate is a small adjustment to this one figure, which is far easier than multiplying by 0.18 in your head.
Building 15%, 18% and 20%
- 20% = double the 10%. The easiest tip to calculate, which is partly why it became the default.
- 15% = 10% plus half of the 10%. On $60: $6 + $3 = $9.
- 18% = 20% minus 2%, and 2% is one-fifth of the 10% figure. On $60: $12 − $1.20 = $10.80.
- 25% = 20% plus half of the 10%. On $60: $12 + $3 = $15.
For an even faster estimate, round the bill to a friendly number first. A $63.40 bill can be treated as $65 — the extra cents cost you a few pennies and buy you a clean answer.
One anchor number, four tips. No calculator, no multiplying by awkward decimals.
Tip table for common bills
| Bill | 15% | 18% | 20% | Total at 20% |
|---|---|---|---|---|
| $25 | $3.75 | $4.50 | $5.00 | $30.00 |
| $40 | $6.00 | $7.20 | $8.00 | $48.00 |
| $55 | $8.25 | $9.90 | $11.00 | $66.00 |
| $80 | $12.00 | $14.40 | $16.00 | $96.00 |
| $120 | $18.00 | $21.60 | $24.00 | $144.00 |
| $250 | $37.50 | $45.00 | $50.00 | $300.00 |
Should you tip on the tax?
Mathematically it makes a small difference. On a $100 meal with 8% sales tax, tipping 20% on the pre-tax subtotal gives $20; tipping on the $108 total gives $21.60. Etiquette guides generally say pre-tax is correct, while most card terminals calculate the suggested tip on the post-tax total — worth knowing when the on-screen "20%" looks higher than you expected.
Service charges and gratuity included
Many restaurants add a service charge automatically, typically 12.5% or 18% for larger parties. If the bill already includes one, an additional tip is optional — you are otherwise paying a percentage twice. Read the line item carefully: "service charge", "gratuity" and "auto-grat" all mean the tip is already in the total.
To work out the food cost from a total that includes service, divide rather than subtract: a $92 total including 15% service came from $92 ÷ 1.15 = $80. That is a reverse percentage, and subtracting 15% from $92 would give the wrong figure.
Splitting the bill fairly
The cleanest method is to total the bill including tip first, then divide by the number of people — everyone contributes proportionally without anyone doing extra arithmetic. A $186 bill with 20% tip is $223.20; split four ways that is $55.80 each.
When the meals differ a lot, split by share instead: each person's tip equals their share of the subtotal times the tip rate. Someone whose food came to 40% of the subtotal pays 40% of the tip.
Practice problems
1. What is an 18% tip on a $73 bill?
2. Three people split a $96 bill with a 15% tip. What does each pay?
3. A bill of $138 already includes a 15% service charge. What was the food total?
4. You want to leave exactly $20 on a $85 bill. What percentage is that?
Frequently Asked Questions
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