How do I split a bill fairly when orders differ?
Tip on the pre-tax total unless local custom says otherwise. Split an uneven bill by charging each person their own items and dividing tax and tip in proportion to those amounts rather than by headcount.
Updated 2026-08-24
What a tip is calculated on
The percentage is the part everyone argues about and the base is the part that quietly changes the answer.
The conventional base in the United States is the pre-tax subtotal. Tax is a government charge that the restaurant collects and passes on, and no service was provided in respect of it, so tipping on it means tipping on a number the restaurant never receives. In a jurisdiction with ten percent sales tax, tipping twenty percent on the post-tax total is effectively a twenty-two percent tip.
That said, the difference is small in absolute terms and plenty of people tip on the total for simplicity. It is a convention rather than a rule, and card terminals frequently compute suggested amounts on the post-tax figure without saying so — which is worth noticing, because those suggestions have drifted upward and a screen offering 25, 30 and 35 percent is anchoring rather than informing.
Service charges are the item to check before adding anything. A charge described as a service charge, gratuity or covert is already a tip, and it is common on larger groups. Adding a further twenty percent on top of an included eighteen percent service charge is a straightforward double payment, and it happens constantly because the line is easy to miss on a long bill.
Norms differ enormously by country and it is worth knowing which model applies. In much of the United States tipping supplements a wage that is legally permitted to be below the standard minimum, which makes it materially different from a discretionary bonus. In much of Europe service is included and rounding up is generous. In Japan and South Korea tipping is not customary and can cause confusion. The percentage is a local convention, not an international one.
Splitting a bill that is not even
Dividing by headcount is the fastest method and is fair only when everyone ordered comparably, which is often not the case.
The itemised method is the fair one and takes very little longer. Each person is charged for what they ordered. Shared items are divided among those who shared them. Tax and tip are then allocated in proportion to each person's subtotal rather than split equally — because tax is levied proportionally and a tip is a percentage of a bill, so someone whose share is a fifth of the food should pay a fifth of both.
The distinction matters more than it looks. On a bill where one person ordered a forty-dollar main and several drinks while another had a fifteen-dollar salad and water, splitting the tip by headcount asks the smaller order to subsidise the larger one twice over — once on the food and again on the percentage. Proportional allocation removes that without any negotiation.
Rounding is the last step and needs a rule agreed in advance, because dividing an odd amount among several people leaves a remainder of a few cents. Rounding each share up and letting the payer keep the difference is simple and slightly favours whoever paid; distributing the remainder to the largest share is marginally fairer and harder to explain. Either is fine; deciding afterwards is what causes friction.
Where a group settles repeatedly over time, tracking a running balance rather than settling every occasion is considerably less work and tends to even out. It also removes the awkwardness of small transfers, which is usually the real obstacle rather than the arithmetic.
Unit price is the only honest comparison
Packaging is designed to make comparison difficult, and unit pricing is the defence.
The unit price is cost divided by quantity — per litre, per kilogram, per hundred grams, per sheet. Reduced to the same unit, two products become directly comparable regardless of how their packs are sized, and the comparison frequently contradicts the impression the shelf gives.
The assumption that a larger pack is cheaper per unit is wrong often enough to be worth checking every time. Retailers know the heuristic exists and price against it, so the family size is regularly more expensive per unit than the medium, particularly when the medium is on promotion. Studies of supermarket pricing find this in a meaningful minority of comparisons, and it is not an accident.
Several tactics make the arithmetic harder on purpose. Pack sizes are chosen not to divide neatly, so 750 grams sits beside 400 and 1.2 kilograms. Units are switched between comparable products, with one priced per 100 grams and another per kilogram. And multibuy offers are framed as a discount without a per-unit figure, which is why three for two on an item whose single price rose last month can be worse than the old single price.
Shrinkflation is the version that moves over time rather than across a shelf. The pack keeps its price and its appearance and loses ten percent of its contents, which is a ten percent price rise that no price tag records. Comparing today's unit price to a remembered pack price will not catch it; comparing unit price to unit price will.
Many jurisdictions require unit pricing on shelf labels precisely because the comparison is otherwise impractical. Where it is displayed, it is usually in small print beneath the headline price, and it is the number worth reading.
Percentage changes do not cancel out
One arithmetic point underlies all of the above and is worth stating on its own, because it produces confident wrong answers.
A percentage increase followed by an equal percentage decrease does not return to the original. A price that rises twenty percent and then falls twenty percent ends up four percent below where it started, because the increase applied to the original and the decrease applied to the larger figure. Reversing a twenty percent rise requires a fall of about 16.7 percent.
This is why a discount off an inflated price is not the same as a discount off the original, and it is the mechanism behind advertised savings that are calculated against a price nobody paid. Regulations in several countries now require the reference price to be the lowest charged in a recent period for exactly this reason.
The related confusion is between percent and percentage points. A rate moving from four percent to six percent has risen two percentage points and fifty percent, and both descriptions are correct. Which one is quoted, without saying which, is a common way to make a modest change sound dramatic or a large one sound minor.