How to Calculate a Tip (Fast Mental Math)

You don’t need an app to leave the right tip. With one simple trick you can work out 15, 18, or 20 percent in your head in a couple of seconds. Here’s the method, a full chart, and the fastest way to split the bill. When you want it exact or need to divide it across a group, the tip calculator handles it.

The formula behind every tip

A tip is just a percentage of your bill, so the math is one line:

tip = bill x (tip percent / 100)

For an 18 percent tip on a $50 bill, that’s 50 x 0.18, which is $9. To jump straight to the total including the tip, multiply by 1 plus the decimal instead: 50 x 1.18 is $59. That’s all a calculator is doing under the hood.

The 10-and-double trick for 20 percent

Here’s the shortcut that makes tipping easy without a phone. Finding 10 percent of any number is simple: just move the decimal point one place to the left. From there you can build the common tips.

• 10 percent: move the decimal one place. $46.00 becomes $4.60.
• 20 percent: find 10 percent, then double it. $4.60 doubles to $9.20.
• 15 percent: find 10 percent, then add half of it. $4.60 plus $2.30 is $6.90.

So on a $46 bill, you’ve worked out that 15 percent is about $6.90 and 20 percent is $9.20, all in your head. Round to a clean number if you like, since nobody minds a tip nudged up to the nearest dollar.

The tip chart: 15, 18, and 20 percent

If you’d rather just read it off, here’s what each common tip comes to across a range of bills.

Bill	15% tip	18% tip	20% tip
$10	$1.50	$1.80	$2.00
$20	$3.00	$3.60	$4.00
$30	$4.50	$5.40	$6.00
$40	$6.00	$7.20	$8.00
$50	$7.50	$9.00	$10.00
$60	$9.00	$10.80	$12.00
$75	$11.25	$13.50	$15.00
$100	$15.00	$18.00	$20.00
$150	$22.50	$27.00	$30.00
$200	$30.00	$36.00	$40.00

Notice the neat trick in the last row: on a $100 bill, the tip in dollars is exactly the percentage. That makes $100 a handy anchor. If your bill is $100 and you want 18 percent, the tip is $18, and you can scale from there.

How to split a tip between people

Splitting is where the math gets fiddly, so here’s the clean way to do it.

1. Work out the tip and add it to the bill to get the grand total.
2. Divide the grand total by the number of people.

Say four of you have a $120 bill and want to leave 20 percent. The tip is $24, the total is $144, and split four ways that’s $36 each. If you’d rather not juggle it at the table, the tip calculator takes the bill, percentage, and party size and shows each person’s share at once.

Those card-machine tip buttons

When the card reader flips around and shows you 18, 20, and 25 percent buttons, it’s doing the same math you’d do by hand, so you don’t have to trust it blindly. Here’s what’s worth knowing so you’re in control.

• The suggested percentages are often on the high side. Plenty of machines now start at 20 or 25 percent, and some quietly calculate the tip on the after-tax total, which nudges it up. There’s nothing wrong with tapping “custom” and entering your own number.
• Counter service is different from table service. You’re not obliged to tip 20 percent for handing over a coffee, so it’s fine to pick a smaller amount or skip it at a counter.
• Check what the percentage is based on. If you want the classic pre-tax tip, the custom field lets you match the numbers from the chart above exactly.

The buttons are a convenience, not a rule. You always get to decide, and now you can check their math in a second.

A quick sanity check

Whatever method you use, a good gut check is that 20 percent should be about a fifth of the bill and 15 percent about a seventh. If your number is way off that, you’ve probably slipped a decimal. For how much to leave in each situation, see the full tipping guide, and for specific services like salons, how much to tip your hairdresser.