In my experience and understanding, investors (almost) always get preferred shares with a liquidation preference. So unless you know what the preferences are, any such calculations are completely bogus. But even if you know them (and note that full cap tables are not commonly shared with employees in my experience) such calculations are still mostly bogus, because:
* You don't know what the preferences of future rounds will be. Your founders may say that they will never go above 1x or whatever, but the company may enter difficult waters and be forced to accept less beneficial terms.
* If you hold common shares in the presence of preferred shares with a liquidation preference, the payout function at acquisition/IPO will depend non-linearly on the selling price. There are steps and there will be a price below you will be 100% wiped out. So the incentives are not aligned. Preferred normally has all the voting rights, and for them 5% more or less on the acquisition price might not be a deal breaker. For for the common, 5% may be the difference between a nice down payment on a home or a 100% wipe out.
Based on this I would always negotiate a market rate salary at a startup company and value the options at $0, with 4 exceptions:
* You're offered to be a co-founder or one of the very first employee (* You're joining a late stage company and based on your industry knowledge you expect the company will do a successful IPO within 12 months. In essence you become a late stage investor in this scenario and your investment is your time.
* You're not in it for the money but instead want to change the world (and you don't mind someone else will make money based on your work if successful). For me personally a company like SpaceX could be in this category.
* You "trust" the founders to have your back and make sure your efforts will be rewarded whatever happens. This is a thin justification, but I could imagine doing it if you have been in business with the same team of founders for multiple times already.