The easiest way to find out your CSED for back taxes is to accurately determine the start date for your tax debt. You have a number of ways to approach this. You can simply look at the date of assessment if you received a Notice of Federal Tax Lien in the past. Your CSED will be 10 years from that date. In addition, it’s possible to get a more official answer by requesting a transcript of your IRS account to obtain information needed to make a calculation based on date of assessment and date of filing.