<prompt> Human: Growing up I was always a pretty aggressive saver. Id put away birthday money, odd job money, etc. I worked all through high school and college and managed to save a bit, which I put into a Roth IRA. My parents had a financial advisor, so I simply let him manage my investments and tried not to worry about it.2 years ago, after finally reviewing my portfolio, I decided that their advisor was too conservative for me 40 in bonds at age 23!, so I arranged for my funds to be moved to Vanguard where I could invest them as I saw fit.Anyway, the letter from the IRS came today, saying that in 2013 I had about 25k in unreported income mostly securities from vanguard brokerage services, plus a couple hundred in taxable dividends. That meant I owed 5k, plus a 1k fee for a Substantial tax understatement penalty, plus interest.Im guessing that when I was trying to convert my portfolio, the old stocks and bonds were sold instead of being exchanged? I dont really know, but Im freaking out a bit because 6k is a huge amount of money to me. I dont know if I have any recourse, though Ill call Vanguard when theyre open next week and ask. Any advise or, if I have no options, sympathy would be greatly appreciated.  <response>: I see this all the time. This is my best guess:When you sold the investments at broker A, they reported the sale to the IRS but didnt report the cost basis. So lets say you sold xx worth of funds, the IRS thinks you have a cost basis of 0 so they claim you owe xx in taxes interest. This is what you need to do:Get the 1099 from broker A and FILE YOUR TAXES to show what your GAIN from these sales were. That should resolve the issue.Im assuming you didnt have a capital gain of 25k. If you really did then you might actually owe these taxes. 