A tip has a base, a rule and a leftover cent

Published 2026-11-04 · Last reviewed 2026-11-06

Splitting a bill looks like one division. It is really two decisions and one leftover: what the tip percentage is applied to, how each person's share is rounded, and who pays the cents that do not divide. A $87.43 bill with 7.25% tax and an 18.00% tip, split three ways, totals $109.51 - and the three people pay $36.51, $36.50 and $36.50. This guide is about where that last cent came from.

A tip needs a base before it needs a percentage

A tip percentage has to be applied to something, and the page names the thing: the pre-tax subtotal or the taxed total. On this bill the tip is $15.74 on the pre-tax subtotal. Taking the same 18.00% from the taxed total would give $16.88, about $1.14 more - roughly 7.2% of the tip itself, which is nothing at one table and a visible disagreement over a year of them.

US tipping guidance generally uses the pre-tax subtotal, because the tax is not part of the service being tipped. Other places quote tips on the total, because that is the number printed at the bottom of the receipt. Neither is wrong; a page that does not say which one it used is only accidentally right. That is why the answer is printed with its base, and why the guide to percentages is worth reading next: the base is the same question wearing different clothes.

Cents are split one at a time, not divided

Dividing $109.51 by three gives $36.5033, which is not money. Rounding each share on its own loses or invents a cent that somebody still has to cover. So the split is done in whole cents instead: everybody gets the same base share, and the remainder is handed out one cent at a time from the top of the list. Three people splitting $109.51 pay $36.51, $36.50 and $36.50 - and the three parts add up to exactly $109.51.

That is the whole promise: the parts equal the whole, and the page says who paid the odd cent rather than pretending the shares are identical when they cannot be. The same arithmetic is what a till does, and it is why the column on the page adds up when you check it by hand.

Rounding up is a decision, so the page prints the difference

Rounding is a separate choice from the base. Four people splitting $71.50 pay $17.875 each, which is not money; rounding each share up to the next dollar means four payments of $18 and $72.00 collected against a $71.50 total. The $0.50 difference is not an error - it is the price of round numbers - and the page prints it rather than quietly keeping it. Rounding each share up to the next cent collects at most one cent per person, which is small enough to be invisible; whole dollars are not, and pretending otherwise is how a table ends up arguing about cash that never existed.

Where these numbers come from

• Every figure above is calculated, not copied in. The tax line, the tip, the total, each share and the rounding difference all come from one shared bill-splitting calculation that works in whole cents. The calculator page and this guide use the same calculation, so a change in one shows up in both or in neither.
• Every release automatically checks the arithmetic: the uneven-cent splits (including the cent that does not divide), the two rounding modes, and the identity that the shares add up to what is actually collected.
• The convention is described, not assumed. Tipping on the pre-tax subtotal is a custom rather than a law, and it differs by country; the page states which base it used and what the other base would have produced, so the reader can apply whatever convention their table actually follows.

What this guide does not cover

It does not tell you how much to tip, and it does not treat a service charge as a tip: a charge added by the restaurant is part of the bill unless it is passed on, and the page says so. It does not model tip pooling, credit-card processing fees or the tax treatment of tips as income - the first two belong to the restaurant, and the third belongs to a payroll page. Nor is it a lesson in floating point: the money here is handled in integer cents precisely so that the arithmetic does not need one.

Split your own bill in the Tip Calculator, check the percentage behind the tip with the Percentage Calculator, or add the tax line properly in the Sales Tax Calculator.

Explanations and estimates only - not financial advice, and not a recommendation about tipping. Read the full disclaimer.