So if it's all still in the 401K account then there is nothing to report on your tax return. So you can't use the losses on your tax return. You only pay tax when you take a withdrawal from the 401K. That's is the benefit of using a 401K or IRA. You don't report the buys and sells, gains or losses or anything that happens inside the account. But then when you take a distribution you pay regular income tax and don't get the capital gains treatment on it.
