You can use your 2013 capital losses to reduce your current year’s income taxes by  applying such losses against your 2013 capital gains. You must however be careful of the superficial loss rules preventing you from claiming a capital loss on an identical asset that you reacquired 30 days before or after the sale date.

If capital gains were realized in the years 2010 to 2012 and net capital losses were incurred in 2013 then you can carry these losses back against previous years’ capital gains. You can carry the unused 2013 losses forward to future capital gains.

The last 2013 transaction date effective for publicly traded securities is December 23, 2013.