Short term and long term sales are reported differently on your tax forms, that’s why we need the Date Acquired and the Date Sold.
In some cases, the reports from your brokerage firm might not include the data acquired date. In these cases, you can provide an estimate:
For short term sales (ie, if bought and sold in the same year), use January 1st of the year the stock was sold.
For long term sales, (ie, you bought the stock more than year before you sold it), use January 1st of the year before it was sold.