is that .75 shares or 75% of all the stock. the IRS can't argue if you use 0 cost. however. if the value added to your w-2 in the year it was taxable, it may be that you are missing out on a substantial capital loss. your other problem is what are you going to do if the rest of that stock is sold. the further in the future the harder it will be to come up with a number. depending on the year, there may be info on the w-2. if you don't have it you can get a copy from Social Security Adm for about $65. the IRS probably no longer has a transcript going back father than 2012
