A 50/50 split feels fair right up until the moment nobody can quite explain why it is 50/50. That is usually when the trouble starts. Not because the number is wrong, but because the reasoning behind it was never said out loud.
The honest truth is there is no universal answer. The right split is a judgment about a handful of things that are different for every team.
Think about contribution: who has built what so far, and who will carry the heaviest load going forward. Think about role and risk: who left a job, who is unpaid, who put money in. Think about commitment and timing: who is full time, and who was there at the very start versus joining once the idea was already working.
Equal can be right. Weighted can be right. Unexamined is the only wrong answer.
An equal split works well when founders genuinely see their contributions as comparable and can say so without flinching. A weighted split works when the difference is real and, just as importantly, understood and accepted by everyone. What does not work is a number nobody can defend a year later.
Whatever ratio you land on, pair it with vesting. The split decides the intended slices of the pie. Vesting decides that each founder earns their slice by actually showing up over time. Together they let the deal survive contact with reality, including the reality that people and circumstances change.
The right split is the one all of you can still defend, calmly, under pressure, a year from now.