If you do not have the original transaction confirmation, the next best thing is to make an educated guess on the cost basis of shares sold. The IRS will presume that your cost basis is zero. As a tax consequence, the sales proceeds of your shares would be reported as a capital gain. I would highly recommend to do a little research to figure out the cost basis of the shares sold. It could potentially save you a lot in taxes.
You can go to the company’s website, Marketwatch, Nasdaq, BigCharts, or Yahoo Finance to find historical high and low prices for the year you know you purchased the shares sold.
If your best educated guess is a date range rather than a specific date, use the historical prices at the start date and end date of that time-frame to come up with an average stock price for that time period. Make sure you keep a record of your calculation in case the IRS would like to know how you came up with your cost basis.
