You can use your 2018 capital losses to reduce your current year’s income taxes by applying such losses against your 2018 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 2015 to 2017 and net capital losses were incurred in 2018, then you can carry these losses back against previous years’ capital gains. You can carry the unused 2018 losses forward to future capital gains.

The last 2018 transaction date effective for publicly traded securities is December 21, 2018.