My 1099 has a section called "Unknown Term Gains/Losses - Report on Form 8949, Part I with Box B or Part II with Box E checked." Date acquired and cost basis fields both say "N/A." I do not have a record of when these shares were originally acquired.
sarah-jane-laven,
Sigh ... a lesson for the future to keep old records. Mine date back to the early 1970s. Anyhow, a couple of initial questions:
(a) was it just one stock (we are talking about stocks [or mutual fund shares?] here) or were there different stocks on that list?
(b) were they inherited or simply purchased some time in the past.
Unknown cost basis
You have to report the sale on your tax return. Lacking any cost basis, the IRS will consider the entire sale amount as taxable. So, you need to make your best effort to determine the original cost basis, even if (worst case) it's a guess. Historical prices of publicly traded stocks are readily available on the internet and should, at least, satisfy the IRS that your basis wasn't zero; just "google" “Historical Stock Prices". I use http://bigcharts.marketwatch.com/historical/. The stockholder relations dept. at the company may be able to help.
Unknown Basis
https://ttlc.intuit.com/community/investments/help/how-do-i-find-a-stock-s-cost-basis/00/25750
Unknown Basis & Date
Well you know it was long term since the broker would know any short term basis ... and the basis is ZERO unless you can figure out a better amount ... use your BEST GUESS based on something you can support in an audit if the IRS was to ever challange your figure.
All good information, guys, and where I was leading, though more slowly as the OP is a newcomer and may not have the background knowledge to grok the details yet. Perhaps I should have claimed the posting, though that freezes out expert contributions such as yours. BTW, I, myself, ran into a situation where a short term transaction was not reported with basis on my brokerage statement. But anyhow, yes, I agree the transactions under discussion were surely long term, meaning held for more than a year. I ask about inherited securities as that could make it a good deal easier to nail down an acquisition date and a valuation as of that date.
We've got your back Sarah Jane!