Another really important, highly negative, combination of these factors is if you want to leave the company. If the company is public, then you can essentially leave whenever you want, exercise the options and sell the stock to pay the costs (exercise price + taxes). But if the company is private, you have to pay the exercise price + applicable taxes (which can exist even if you only have theoretical gains) yourself,…
Just a heads up, the 90 day out clauses are usually put in there by the company lawyers. The only rule the IRS has is that ISO options flip to NSO after 90 days[0]. Take a look at the Pinterest options plan[1], where Pinterest actually gives you 7 years from when you leave to exercise. Your ISO options just flip to NSO after 90 days. [0] http://www.mystockoptions.com/faq/index.cfm/catID/36274DB1-D... [1] http://fortu…
One not-as-obvious reason why companies are reluctant to set long expiration dates on options is because it means former employees take up space in the cap table even if they have no intention of ever exercising that option. The company essentially has to treat those shares as having been purchased, without having received any cash for said purchase. Cap table cruft can make it harder to negotiate subsequent funding rounds.