The short answer is no, an individual may not carryback capital losses. 26 USC 1212
(b) Other taxpayers
(1) In general If a taxpayer other than a corporation has a net capital loss for any taxable year—
(A)
the excess of the net
short-term capital loss over the net long-term capital gain for such
year shall be a short-term capital loss in the succeeding taxable year,
and
(B)
the excess of the net
long-term capital loss over the net short-term capital gain for such
year shall be a long-term capital loss in the succeeding taxable year.
Your question implies this is investment income and losses. Therefore the above answer would stand.
If you are in the trade or business of being a broker, trader in securities, or in the trade or business of dealing in securities for your own account, the answer would be different. It would qualify as a business loss, giving rise to a net operating loss that could be carried back.
It is a high hurdle to claim trade or business for your own account. The IRS does provide guidance. Note that if you claim it for losses, you also have to claim it for gains, thus subject to ordinary earnings and self-employment tax.
https://www.irs.gov/taxtopics/tc429.html
**Disclaimer: Effort has been made to offer correct information; but due to the discussion forum limitations, the poster disclaims any legal responsibility for the accuracy of the poster's response**
