The even split, and why it rarely lands cleanly

The arithmetic looks trivial:

each person = (subtotal + tax + tip) ÷ number of people

The complication is that money has two decimal places and division usually does not. A total of 87.43 between three people gives 29.14333…, and if everybody pays 29.14 the table is one cent short.

The fix is to work in whole cents and distribute the remainder rather than rounding each share independently:

Rounding each share up instead produces 29.15 × 3 = 87.45, a two-cent overpayment. Rounding each down leaves the payer short. Remainder distribution is the only method that always reconciles exactly, and it is what a correct splitter does silently.

The itemised split, done properly

When people ordered different things, the fair approach is that each pays their own items plus a proportional share of tax and tip — not an equal share of them, because tax and tip both scale with what was ordered.

Three diners:

Tax at 8.5% is 6.29. Tip at 18% of the pre-tax subtotal is 13.32. The grand total is 93.61.

There is a shortcut that avoids computing three percentages. Divide the grand total by the subtotal once to get a single multiplier, then apply it to each person:

multiplier = 93.61 ÷ 74.00 = 1.265

It reconciles to the cent here, but check it every time — when it does not, the difference is a cent or two and is settled by the remainder rule above.

Tip before or after tax

On the same bill the choice is not trivial:

Just over a dollar apart, and about 8% more tip. Tipping on the pre-tax amount is the traditional convention, on the reasoning that you are rewarding service rather than the tax authority. Card terminals increasingly compute their suggestions on the post-tax figure, which quietly raises every percentage on the screen.

The shared-plate problem

This is where splitters usually break down, because it is a question about the table rather than about arithmetic. A shared appetiser has no owner. Three workable conventions:

• Split the shared items among the people who ate them, then run the itemised method on the resulting per-person figures. Most accurate, most fiddly.
• Fold shared items into the subtotal and split them evenly, keeping individual items itemised. A good compromise, and what most groups do without saying so.
• Split everything evenly and accept the unfairness, which is often the right social answer for a bill where the spread is small.

The one case where an even split is clearly wrong is alcohol. Drinks are frequently the largest and most unevenly distributed part of a bill, and in many places they are taxed at a different rate, so a non-drinker paying an even share can be subsidising a substantial amount.

The percentage that keeps moving

Worth knowing if the suggested figures ever feel high: the standard tip is not a fixed custom. In the middle of the twentieth century 10% was normal in the United States; 15% became the default by the 1980s; 18 to 20% is the common floor now, and card terminals often present 20, 25 and 30. Part of that drift is straightforward anchoring — a default option shifts the average choice toward it, and the presets are set by the merchant, not by any standard.

The convention is also strictly local. Service is frequently included in the bill across much of continental Europe, where a small round-up is the norm rather than a percentage. In Japan tipping is not customary and can cause confusion. And a mandatory service charge is not a tip at all — it is a line item on the bill, and whether it reaches the staff depends entirely on the establishment, so it is worth asking before adding a further amount on top.

Honest limits

A splitter can only divide the numbers you give it. It does not know who ordered what, cannot see a discount that applied to one dish, cannot apply the different tax rates that some jurisdictions levy on alcohol or prepared food separately, and cannot judge whether an even split is the socially correct answer.

Currency rounding is a real edge case. Where the smallest coin is larger than the smallest accounting unit — Canada after the withdrawal of the penny, Switzerland with its five-centime coin — cash totals round to the nearest available coin while card payments do not, so the cash and card versions of the same split differ by a few cents.

Questions people actually ask

Someone only had a soda. What is fair?

Itemise. Take their drink out, apply the multiplier method to everyone including them, and the tax and tip fall out proportionally without anyone having to negotiate.

Why does one person pay a cent more?

Because the total does not divide exactly. Distributing the leftover cent to one payer is the only way the payments sum to the bill; the alternative is for the table to be short or over.

Should the tip be a percentage of the bill at all?

It is a convention rather than a rule, and it has the odd property that a bottle of wine attracts more tip than a plate of food requiring more work. Some diners tip per person or per course for that reason. The tool will compute whatever basis you prefer.

Is any of this stored?

No. Every figure stays in your browser and nothing is transmitted or saved.