You can use your 2008 capital losses to reduce your current year’s income taxes by applying such losses against your 2008 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 2005 to 2007 and net capital losses were incurred in 2008 then you can carry these losses back against previous years’ capital gains. You can carry the unused 2008 losses forward to future capital gains.
The last 2008 transaction date effective for publicly traded securities is December 24, 2008.