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6.1

Work out a tip in your head

Find 10% by moving the decimal point one place left, then build every other percentage from that.

An older couple paying a waiter at a restaurant table.
Photo: Yan Krukau / Pexels
Area: InformationFrom age 12Time to learn: 10 minutes, then a week of practice on real receipts

You will work out 15% and 20% of any bill in a few seconds without a phone.

Why it matters

Tip screens now ask you to choose a percentage on the spot, and the same math works for discounts and taxes. In the US, tips are a large part of many service workers' pay: federal law lets employers pay tipped workers a cash wage of $2.13 an hour, as long as tips bring them to at least $7.25, and many states require more (US Department of Labor). In Canada, pay rules for servers are set by each province. In a 2023 Pew survey, 57% of US adults said they would tip 15% or less for an average sit-down meal (self-reported).

How to do it

  1. Round the bill to an easy number. $47.80 becomes $48.
  2. Find 10%: move the decimal point one place to the left. 10% of $48 is $4.80.
  3. Find 20%: double the 10%. $4.80 x 2 = $9.60.
  4. Find 5%: take half of the 10%. Half of $4.80 is $2.40.
  5. Find 15%: add the 10% and the 5%. $4.80 + $2.40 = $7.20.
  6. Round to a tidy amount if you like, such as $7.25 for 15% or $10 for 20%.
  7. Decide whether you tip on the amount before or after tax. It changes the tip a little; the choice is yours.
  8. Practice on a new number: 10% of $63 is $6.30, so 15% is $9.45 and 20% is $12.60.

Common mistakes

  • Moving the decimal the wrong way and getting $480 instead of $4.80.
  • Doubling to get 15%. Doubling gives 20%; 15% is 10% plus half of it.
  • Not rounding first, which makes mental math harder than it needs to be.
You can do this when …you can say 15% and 20% of $36.50 within 10 seconds: about $5.50 and $7.30.

Sources

  1. Pew Research Center - Tipping culture in America
  2. US Department of Labor - Fact Sheet #15: Tipped employees

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6.2 → next lesson: Why gift card payment means scam
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