first, for 2017 you have to determine if you have an NOL by completing schedule A of form 1045, having a loss on Schedule C does not mean you have an NOL. assuming you do, then, if you timely filed your 2017 return you needed to elect to carry forward the NOL. if you didn't timely file it or failed to make the election, the NOL had to be carried back to 2015 and then any remaining to 2016 and any remaining from 2016 to 2018. note that it's too late to file an NOL carryback claim for 2015 -16 . they had to be filed within three years of their due date or if extended their extended due date (2015 if extended by 10/15/2019 and 2016 if extended by 10/15/2020. you must treat the 2017 NOL as if it has been carried back even though you can't get a refund for those years. any remaining NOL can be claimed for 2018.
