Yes and here is the reason: When you sell stock, you receive a 1099 B. Not only do you receive it but a copy also goes to the IRS. Until you file a tax return, the IRS may not know if you have a gain or a loss. Your tax return contains not only what you received from the sale but also what you paid for the stock. It provides informatiion showing that you indeed had a loss. You can take up to $3,000 in losses against income in any year and excess losses can be carried over to future years when your income may be higher. Also many 1099-B's do not always contain cost data so the irs has no idea what you paid until you tell them. Without a tax return then can consider a zero basis and a gain on the stock. Hope this helps.