You will need to enter a "Date Acquired".
If the "Date Acquired" field is blank on your Form 1099-B, it means the Payer didn't have that information. You would need to provide an answer from your records or enter a date that is consistent with the holding period.
If you held the security for more than 1 year, then enter a
"Date Acquired"
that is more than 1 year before the date you sold the security.
If you held the security for less than 1 year, then enter a
"Date Acquired"
that is less than a year before the date you sold the security (1/1/2015 will work).
If you aren't sure how long you held the security, try looking for the "Box" or "Code" on your 1099-B.
If Box A or B is checked, then the holding period was less than one year.
If Box D or E is checked, then the holding period was more than one year.
