Purchase also starts the clock for determining the difference between long- and short-term capital gains. This is (currently) a big deal for federal income tax.
Taxes on the difference between the purchase price and the "value" on the purchase date is what caused a lot of people problems during the dot-bomb. They exercised in the money options, owed taxes, and couldn't pay them when the stock price dropped. (Many of them were trying to hold out for long-term capital gains rates. Oops.)
Note that CA taxes both long- and short-term capital gains at the same rate. Jim Clark says that's why he no longer lives in CA.
Taxes on the difference between the purchase price and the "value" on the purchase date is what caused a lot of people problems during the dot-bomb. They exercised in the money options, owed taxes, and couldn't pay them when the stock price dropped. (Many of them were trying to hold out for long-term capital gains rates. Oops.)
Note that CA taxes both long- and short-term capital gains at the same rate. Jim Clark says that's why he no longer lives in CA.