https://tldroptions.io/ has collected various estimates and averages relating to how much startups raise and how much employees stand to make from stock options (the following is mostly quotes):
~65% of companies will never exit, ~15% of companies will have low exits* ("any exit for less than the average amount raised by a successful startup"), ~20% of companies will make you money
estimate of how much an employee will make: (Exit Price < Money Raised) ? $0 : (Exit Price * Diluted Percentage / 100) - (Current Fair Market Valuation * Current Percentage / 100)
estimate the company will exit after raising exactly four rounds of financing.
estimate the company will raise $41 million before exit, which someone once said was average amount raised by a successful start up, and those investors all had 1x liquidation preferences.
estimate the dilution will be 35% per round.
estimate that the valuation grows 3x per round plus 35% at exit and that the Fair Market Valuation is 40% of this plausible current valuation.