A fair split should consider what people actually agreed to share.

Splitting evenly is simple, and simple is not the same as fair. One person ordered within what everyone discussed while another added things nobody expected, and an automatic division moves the cost of that choice onto people who did not make it. What was agreed matters more than what is easy to calculate.

Say how the bill will work before anyone orders, in one light sentence. Doing it early is easy. Doing it while the card is on the table is not.