<prompt> Human: Hi PF,In 2013, I exchanged all of my index funds to a target fund to make it easier for me to manage. I did received a 1099-B from Vanguard and my capital loss for that exchange is something less than 450. This loss is small so I did not think of reporting it on my tax returns. I know that since 2012, the cost basis is included in both forms that were sent to the IRS and I. What are the chances that the IRS will ask me to amend this 2 or 3 years down the road? Can they still use the cost basis of 0 even though the information Vanguard sent already has the cost basis listed? I just dont want to be hit with a capital gain in the thousands of dollars if they use the cost basis of 0. EDIT: Thanks all, it looks like Im worrying over nothing. I will look into filing an amended return.  <response>: If you realized losses, wouldnt you have been able to write this off? 