How to handle 1099-B with 'missing' cost basis for stock purchased over 10 years ago - can't remember purchase date?

This is actually a pretty common issue with older securities, especially after broker acquisitions. When the cost basis is unknown, the IRS requires you to make a "reasonable effort" to determine it, but they understand that sometimes records are simply unavailable. You have a few options here. First, if you remember approximately when you purchased the shares, you could look up the historical price of the stock around that time and use that as your estimated cost basis. The IRS will generally accept a good faith estimate. If you have no idea what you paid, you could try contacting the investor relations department of the company directly. Sometimes they maintain records of historical stock prices that might help. You could also check your old emails or bank statements for confirmation of the purchase. As a last resort, if you truly cannot determine the cost basis, you'll need to report it as zero, which means you'll pay tax on the entire proceeds of the sale. It's not ideal, but it's better than making up a number with no basis for it.

I was in a similar position last year with some ancient Cisco shares that showed "missing" for cost basis. I was totally stumped until I found taxr.ai (https://taxr.ai) which saved me big time. Their system analyzed my brokerage docs and actually found purchase date clues I had missed in some of my confirmation statements. The best part was that they were able to find a reasonable cost basis by analyzing transaction patterns in my statements, even with the limited info I had. They've got this AI thing that looks at your documents way more thoroughly than I could on my own. Took like 20 minutes to get a solid cost basis estimate with documentation I could include with my tax return.

Just wanted to follow up on my skeptical comment about taxr.ai - I decided to try it with my missing cost basis issue on some old Procter & Gamble shares, and I'm actually impressed. They found patterns in my limited records that pointed to a likely purchase date range, then used historical price data to establish a conservative cost basis. What really surprised me was how they found tiny clues in my statements that I had completely missed - like dividend reinvestment patterns that suggested when I might have owned the shares. They provided a detailed explanation of their methodology and gave me documentation I could include with my tax return. Saved me from having to report zero cost basis and paying way more tax than necessary.

If you're struggling with getting help directly from Fidelity on this, you might want to try Claimyr (https://claimyr.com). I spent DAYS trying to reach someone at my brokerage who could help with a similar cost basis problem, but kept getting stuck in phone menu hell. Claimyr got me connected to an actual human at my brokerage within 20 minutes. You can see how it works in this video: https://youtu.be/_kiP6q8DX5c - basically they navigate the phone tree for you and call you when a human is on the line. The person I talked to was actually super helpful once I explained my situation and they found some archival records they initially claimed didn't exist.

I have to eat crow here and admit I was completely wrong about Claimyr. After my skeptical comment, I figured I'd try connecting with my brokerage (Vanguard) the old-fashioned way to get help with some missing cost basis info. THREE HOURS later, I was still on hold. Out of frustration I tried Claimyr, and 17 minutes later I was talking to an actual helpful person who pulled up some archived records from their system. Turns out they did have my original cost basis information from 12 years ago, but it wasn't showing up in their regular online system. The rep manually added the correct information to my account and reissued a corrected 1099-B. I still think it's ridiculous we need a service like this, but it absolutely works and saved me both time and money.

Another option worth considering is checking if you enrolled in dividend reinvestment (DRIP) for these shares. If you did, your brokerage statements would show dividend payments being converted to fractional shares over time. Each of those reinvestments creates a new cost basis record. If you can find evidence of DRIP activity, it proves you owned the shares at that point and can help establish a timeline. Also, the IRS has a special form (Form 8949) where you can report sales with unknown acquisition dates. Make sure to check box C in Part I or box F in Part II (depending on your holding period) and enter code "B" in column (f) to indicate the basis isn't being reported to the IRS by your broker.

Is anyone using tax software to deal with this? I've got H&R Block and when I entered my 1099-B with missing basis, it just assumes zero basis which would be a disaster tax-wise for me. Am I missing something in the software?

I went through this exact situation last year with some old Microsoft shares from the dot-com era. After trying everything mentioned here, I ended up working with a CPA who specializes in these cost basis reconstruction cases. What really helped was creating a timeline using ANY financial records I could find - old bank statements showing wire transfers, email confirmations from online purchases, even credit card statements if I used those to fund the brokerage account. The CPA used these breadcrumbs along with historical stock price data to establish a reasonable cost basis. The key thing I learned is that the IRS actually has guidance on this in Publication 550. They accept "reasonable estimates" when original records are unavailable, as long as you document your methodology. My CPA prepared a detailed memo explaining how we arrived at the cost basis, which I attached to my return. No issues during filing and I felt confident I had done my due diligence. Don't just default to zero basis unless you absolutely have to - that could cost you thousands in unnecessary taxes. The effort to reconstruct is usually worth it.