Bill Split Calculator
Dividing by the number of people is quick and wrong whenever one person had the tasting menu and another had soup. This works out both, so you can see what an equal split actually costs the person who ordered least.
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Formula
Equal is not the same as fair
An equal split is fair when everyone had roughly the same. It stops being fair the moment one person orders two courses and a bottle while another has a starter and tap water — and the person who ordered least is usually the one least likely to say anything.
Seeing both numbers side by side settles it without anyone having to make a point of it. If the difference is a couple of units, split equally and stop counting. If it is twenty, the itemised split is the honest one.
Shared items belong to everyone
Wine, bread, sides and the cover charge are shared regardless of who reached for them, so they divide evenly and then each person adds what they ordered themselves. That is the split most groups actually intend, and it is easier than itemising every glass.
The tip follows the share
A tip calculated on the total and then divided equally moves money from the light eaters to the heavy ones a second time. Here it is added in proportion, so someone paying a third of the bill pays a third of the tip.
Splitting other things by share
The same arithmetic works for rent by room size, a holiday house by nights stayed, or a shared car by kilometres driven. Put the total in, and put your own share in as your items with the fixed costs as the shared part.
Rounding, and who absorbs it
Rounding each share up leaves a small surplus, which is convenient when one person is paying the restaurant and collecting from the others. Rounding down leaves a shortfall that the payer covers. Neither matters much on one evening; it is worth being consistent about with people you split things with regularly.
Frequently asked questions
When is an equal split reasonable?
When the difference between the equal share and the itemised one is small enough that nobody would raise it. The calculation shows exactly what that gap is.
How should the tip be divided?
In proportion to what each person is paying. Dividing it equally on top of an itemised split partly undoes the point of itemising.
Can I use this for rent?
Yes. Put the total rent in, the shared costs such as utilities in the shared field, and your room's share as your own items.
What about someone who only had a drink?
Enter their drink as their own items. They still pay their part of anything genuinely shared, which is normally what people intend.