[ta1234567890]

Day 1 or even Week 1 might be a very unrealistic timeline for most new companies to split equity.

Majority of people starting a new company are very unfamiliar with equity splitting, vesting and everything related to theses things. On top of that, usually the team members aren't even well defined yet, same as the idea for the company.

A lot will change even in the first 6 months of a company that would justify different equity splits for different members that are still founders but join with different (implicit) roles and at different times.

Sadly, unless the founders are extremely lucky, it will probably take them a lot of experience and maybe going through failing a few times until they get the equity split right from the get go for a new company.

And there's a bunch of other external and unpredictable factors. For example: about 4 years ago I started a company with a couple other people - each founder joined at different times and had different amounts of equity - a few months after winning a hackathon, incorporating the company, raising some angel money and getting our first few clients, we applied to YC, got an interview and then got an offer to join YC, but one of their partners wanted us to change the cap table to remove some of the people that had equity and re-split the equity among a subgroup of the founders. We couldn't do it, so they withdrew the offer to join.