I'm not sure if you're asking an "how to" question or really asking an "how much" question.
As to "how to" - I'm assuming the here the 1099-B has a blank in the basis box and is reporting the security as noncovered - then you simply type in the basis as you fill out TurboTax's default 1099-B entry form, (assuming you know it.) No need to resort to any "guide me step by step" path through the interview here.
As to "how to" - this time assuming the 1099-B has an incorrect number in the basis box and is reporting the security as covered - then you type in the 1099-B exactly as it reads, click the blue "I'll enter additional info on my own" button and on the next page enter the correct basis, (assuming that you know it.)
As to "how much" - assuming the option was a NonQualified Stock Option (NQSO) - then your per share basis is the same as the per share "fair market value" used by your employer to calculate the compensation created by your exercise of the option, i.e.,
Compensation =
(GROSS # of shares exercised) x (per share "fair market value" used by employer - per share exercise cost)
As to "how much" - assuming the option was an Incentive Stock Option (ISO) and the sale was a Qualified sale, (sold more than 2 years after the grant date an more than a year after exercise) - your per share basis is the same as the per share exercise price.
(There's yet another "how much" answer if the option was an ISO and the sale was a Disqualified sale, but I'm assuming that the "previous" employer" reference puts it far enough in the past to make this moot.)
Using the "Stocks, Mutual Funds, Bonds, Other" interview, in all cases you'll start by simply transcribing the 1099-B into TurboTax's 1099-B entry form. You CAN GET help with both the "how to" and "how much" questions by clicking the "Guide me step by step" button and then selecting the correct interview for the type of option in question.
Tom Young
