I just did this! If your broker doesn't have the information (if these are non covered shares = not tracked by brokerages previous to 2012 - 2016 depending on whether it is a stock, a mutual fund or a bond)
You will need to have saved your trade confirmations along with any dividends reinvested previous to when the broker started tracking.
If you have changed institutions the current brokerage house may not have your cost basis.
It is vital to keep trade confirmations (taxable accounts)
IF they stock has spit / merged / been bought out.... you have some archeological work to do.
I have another post on HP and related adventures. (do a search on Turbo tax for more information... and for an example you can check out HP Alumi information.
I have never sold any of it (2001 purchase) I have ended up with 6 stocks one of which was bought out in 2021 (perspecta.) To find the cost basis I had to follow all the splits and spin offs back to 2001.
If your stock was a spin off, you do have a cost basis. If you bought previous to 2012 you have to determine it yourself. Statements, Trade confirmations, Fees, GOOD LUCK You will learn something for the future.
My bet is that you do have a cost basis. I did all the work for $13.00 and a good lesson! If you have minimal gains, just be aware for the future or you will be paying more in tax than you need. And worst case is that that income that shouldn't be income bumps you into a higher tax bracket. This can be extremely painful when you are on medicare and after retirement if it affects your income related adjustments charged by social security for medicare.
