The per-share price the IRS treats as the true current value of a company's common stock (Fair Market Value), used to set option strike prices and calculate how much tax you owe when you exercise.
Independent firms like Carta, Aranca, and Scalar use a mix of the income approach (discounted cash flows), the market approach (comparables), and the option-pricing method on the latest preferred round to back out a common-stock price. The FMV usually lands at twenty to thirty percent of the preferred share price for an early-stage company.