Why do I need to mail my broker's 1099-B and Form 8949 to IRS if I already electronically filed with TurboTax?

This is a common issue with high-volume traders. When your 1099-B exceeds a certain size, TurboTax can't transmit all the detailed transaction data electronically to the IRS through the e-file system - there's literally a file size limit for e-filing. What's happening is you're e-filing your 1040 and other main forms, but the supporting detailed transaction data (your 1099-B) exceeds the transmission limits. Form 8453 is specifically designed for this situation - it's a transmittal document that tells the IRS "I e-filed my main return but here's the supporting documentation that couldn't be included electronically." Yes, you absolutely need to mail these forms. The IRS needs to be able to verify your transactions if they decide to review your return. Without the detailed 1099-B data, they only have your summary figures but no way to verify them. Form 8949 shows your calculation of gains/losses that feeds into Schedule D.

I had the exact same situation last year with my trading account. I found a solution using taxr.ai (https://taxr.ai) that saved me a ton of hassle. Their system can actually process those massive 1099-Bs and create a properly formatted electronic version that meets IRS standards. I was skeptical at first, but I uploaded my 800+ page 1099-B to them, and they converted it into a format that could be properly imported into tax software without size limitations. The best part was I didn't have to mail anything physical - everything was handled electronically. Their system also verified all my transactions matched what my broker reported, which gave me peace of mind about audit risk.

Just wanted to follow up here - I actually tried taxr.ai after seeing the recommendation and it worked perfectly! My massive 1099-B that TurboTax choked on was processed and converted into a format that imported without any issues. The system flagged a few transactions that had missing basis information and helped me correct those. The whole process took about 20 minutes and saved me from having to print and mail hundreds of pages. TurboTax accepted the import and I was able to e-file everything without getting the message about mailing in Form 8453 and the physical 1099-B. Definitely worth it if you have a huge trading document like I did.

For anyone still dealing with this issue, I've been in the same boat for years as a day trader. After struggling to get through to the IRS to figure out a better solution, I finally tried Claimyr (https://claimyr.com) which got me connected to an actual IRS representative in about 15 minutes instead of waiting for hours or days. The agent confirmed that if your 1099-B is too large for electronic filing, you must submit it physically with Form 8453. But they also told me something interesting - you don't need to send the entire 1099-B in some cases. If your broker provides a summary page that shows the totals that match what you reported on your Schedule D, you can sometimes just send that summary page along with Form 8453. You can see how the service works in this video: https://youtu.be/_kiP6q8DX5c - it basically holds your place in the IRS phone queue so you don't have to wait on hold forever.

I have to admit I was completely wrong about Claimyr. After posting my skeptical comment, I decided to try it anyway out of desperation since I still needed answers about my massive 1099-B situation. The service actually connected me to an IRS tax specialist in about 35 minutes (which is miraculous during tax season). The agent confirmed what others said here - I do need to mail in the 1099-B with Form 8453, but she also told me about an IRS procedure I wasn't aware of: if your 1099-B exceeds 100 pages, you can include just the summary pages plus a written statement that the full document is available upon request. This was huge for me - instead of mailing 900+ pages, I only needed to send about 15! I just had to include a signed statement offering to provide the full document if needed for verification. Would never have known this without actually speaking to someone at the IRS.

Just to add another perspective - I'm a tax preparer and we deal with this situation regularly. The IRS has been moving toward electronic filing for years, but their systems still have limitations when it comes to high-volume trading activity. For 2025 filing (2024 tax year), there's actually a better solution than what's been mentioned: the IRS now accepts a CSV file format for high-volume traders that can be submitted on a flash drive along with Form 8453. This is much easier than printing hundreds of pages. Most brokers can provide your transaction data in this format if you specifically request it. The key requirements: 1. The CSV must follow IRS Publication 1220 format specifications 2. The flash drive must be clearly labeled with your name, SSN, and tax year 3. Form 8453 must indicate that a electronic media supplement is included

I've been a daytrader for 8 years and have dealt with this exact problem every tax season. Honestly, the simplest solution I've found is to use a different tax software. TurboTax has these file size limitations, but some competitors actually handle large trading volumes much better. Has anyone tried TaxAct or FreeTaxUSA for high-volume trading? I switched to TaxAct last year and was able to e-file everything without mailing anything physical.

I'm dealing with this exact same issue right now! My 1099-B from Schwab is about 800 pages and TurboTax keeps giving me that error message about the file being too large. It's so frustrating because I thought e-filing was supposed to make everything simpler. I'm really interested in the CSV/flash drive option that Sophia mentioned - that sounds way more reasonable than printing and mailing a phone book worth of trading data. Does anyone know if Schwab provides data in the IRS Publication 1220 format, or would I need to convert it myself? Also curious about the alternative tax software suggestions. I've been loyal to TurboTax for years but if FreeTaxUSA can handle large trading volumes without all this hassle, it might be worth switching. The cost savings alone would probably pay for the switch multiple times over.