Add the items from the receipt and tick who shared each one. Service and tip are shared in proportion to what each person ordered, so the friend who only had a salad doesn't pay for the wine.
Using the bill above, here's what each person would pay with an even split compared with paying for what they had. The bars show who's subsidising whom. Sometimes it's a few pence and not worth the fuss; sometimes it isn't.
Pick who put their card down. Everyone else gets one transfer to make, with a reference you can copy into a banking app.
Exact shares rarely land on whole pennies, so someone has to round. Rounding each share on its own can collect a penny too much or too little. Five real methods are applied below to the same shares, in integer pennies, with the total checked against the bill.
The usual shortcut matches the biggest creditor with the biggest debtor until everyone is square, which never takes more than one transfer fewer than the number of people. The true minimum comes from splitting people into the most groups that already balance among themselves; finding that is NP-hard in general, so it’s solved here exactly by searching every grouping.
Riders leave a taxi at different stops, so the fare depends on who travels furthest. The Shapley value (1953) charges each rider their average extra cost over every order in which the group could have formed. For a shared route it reduces to a simple rule: each stretch of road is shared equally by everyone still in the car. It’s computed below by that rule and by brute force over every ordering.
Customs vary more than the maths. The last column applies each country’s typical rate to the food on the bill above.
Neighbouring calculators, with a typical result for each.