Do you tip on the total before or after tax?

Convention in the United States is to tip on the pre-tax subtotal, though many people tip on the post-tax total because it is easier and the difference is small. On an 84.50 bill the gap between the two is usually well under a dollar.

How much is an 18% tip on 84.50?

15.21. Multiply 84.50 by 0.18. The total with tip is 99.71, which is 33.24 each when split three ways.

How to split a bill with tip

17 July 2026

Short answer. Multiply the bill by the tip percentage, add that to the bill, then divide by the number of people. An 84.50 bill at 18% has a tip of 15.21, a total of 99.71, and comes to 33.24 each between three. Round each share up, not down, or the table pays less than the total.

The three steps

Bill              84.50
Tip 18%           84.50 × 0.18  =   15.21
Total             84.50 + 15.21 =   99.71
Split 3 ways      99.71 ÷ 3     =   33.236666...
Per person        33.24

That is the whole thing. The only place it gets interesting is the last line, where the division does not come out even.

The cent that goes missing

99.71 divided by three is 33.236666… repeating. It never terminates, so somebody has to round, and the direction matters:

Each pays	Table pays	Against the 99.71 total
`33.23` (rounded down)	99.69	2 cents short
`33.24` (rounded up)	99.72	1 cent over

Round up. The extra cent lands in the tip, where nobody minds it. Round down and the card gets declined for a two cent shortfall, which is a very stupid way to end a dinner.

This is also the exact scenario where a calculator quietly lying to you costs real money. If the app rounds 33.236666… to 33.24 and then also stores 33.24 as its internal value, adding those three shares back gives 99.72 and the total no longer matches the bill. That drift has a name, and it is why arithmetic that stays exact until the moment it is displayed is worth caring about.

Before or after tax?

The convention in the United States is to tip on the pre-tax subtotal. In practice most people tip on whatever number is printed largest, because the difference is usually under a dollar and nobody wants to do two calculations at a table. Either is defensible. Tipping on the pre-tax amount is the one you can argue for.

Doing it in your head

You rarely need the exact number, only a number that is not embarrassing. For 18%, take 10% by moving the decimal one place left, halve that for 5%, halve again for 2.5%, then add:

10% of 84.50   =  8.45
 5%            =  4.23
 2.5%          =  2.11
──────────────────────
17.5% ≈           14.79   (close enough to 18%)

For 20% it is easier still: move the decimal one place and double it. 84.50 → 8.45 → 16.90. That is why 20% has quietly become the default tip in the US. It is not generosity, it is arithmetic that fits in your head.

Prism Calculator splitting an 84.50 bill with 18% tip three ways, showing 33.24 per person — The same sum, without the mental arithmetic.

Or let it do the rounding

Prism has a tip and split calculator built in, along with six others. Free, no subscription. See the app.