When you sell stocks that you've acquired via an ESPP, such a sale can create "compensation" income that can be included on your W-2, (or not, depending on the circumstances), and you need to add the compensation to your "out of pocket" cost for the stock. Your basis is not simply the discounted price that you paid, though this very likely is the basis the broker has reported on the 1099-B.
If the sale of the stocks did create compensation reported on your W-2 and you don't add the appropriate amount to your out of pocket costs when reporting the sale then you're reporting the same income twice; once as compensation income and then again as an overstatement of gain on sale.
If you know the correct amount of basis to use then enter the 1099-B exactly as it reads and then click the blue "I'll enter additional info on my own" button. On the next page enter the correct basis in the "Corrected cost basis" box.
But if you are unsure of the correct amount of basis to use for the sale then go back to that sale, ask TurboTax to "Guide me step by step" and tell TurboTax that you're selling stock acquired through an ESPP. That's where the Form 3922 information gets entered and TurboTax uses that information to calculate the correct amount of basis.
Tom Young
(SINCE THE DEVELOPERS CHANGE THE SECURITY SALE INTERVIEW EVERY SINGLE YEAR I'LL NOTE THAT THIS ANSWER'S DIRECTIONS ON HOW TO CORRECT THE BASIS FOR THE SALE PERTAINS TO THE 2016 INCOME TAX YEAR. I'M SURE THAT THE INTERVIEW WILL CHANGE IN THE YEARS AFTER THAT.)
