I know nothing about Twitter, but in general it's simple. If there are 199 employees, you can't give the 200th more than 0.5%, else that would be unfair, right?

I know nothing about Twitter, but in general it's simple. If there are 199 employees, you can't give the 200th more than 0.5%, else that would be unfair, right? That person would have to be something really special, like a CEO or VP, to expect more when coming to the party so late. So that's the absolute maximum ceiling. Usually about 10 to 30% of the company is reserved for employees (the rest goes to the founders and investors --- mostly investors, by this stage). So employee #200's theoretical maximum is down to 0.15% or 0.05%. And she's not going to be the last. Over time more investments and employees mean you get diluted more and more. So do the math yourself, but remember that there are a lot of other factors, like taxes, specific skills, etc etc. If you get acquired, it's not as though they write big novelty checks and hand them out like it's a golf tournament. You exchange startup stock (some of it unvested!) for other-company stock. Risk, impact, autonomy and reward are remarkably correlated to how early you join. But if you are in it for just one of those four things you might have a hard time adjusting to the rest.