[fennecfoxen]

Yeah, the standard ESPP I’ve seen (twice now) is essentially a series of call options (at 6, 12, 18 and 24 months in the future). If the option is not 15% in the money at vesting, the plan resets and it is replaced by one that is in the money.

Look at the price for actual call options at these intervals and you will have an approximate idea of the value of this financial instrument. It’s probably substantial, almost certainly more so than the opportunity cost on your money (unless you must meet critical expenses or pay off credit card debt). And if you always sell the same day you buy, the risk is quite low (if the plan is at its bottom and the stock price falls 15%, basically, but most ESPP dates are just after earnings which limits the types of surprises you’re in for).