Our 1099B has no net cost for some of our stock sales

[DDollar · Accepted solution]

You will have to come up with the cost basis for those stocks.  If you inherited them, your basis is the stock price on the date of death.  If they were gifted, your stock basis is the same as the person that gifted it to you.  If you cannot determine the stock basis, you can look up the all time low for the stock and use that.  Finally, if you can't come up with the basis you will have to use zero.