Do I need to file Form 1040X along with an updated 1040, or is the 1040X form by itself sufficient?

You only need to file Form 1040X (Amended U.S. Individual Income Tax Return) by itself. You don't need to prepare and submit an entirely new 1040 form along with it. The 1040X is specifically designed to make corrections to your original return. For your situation with the missed 1099-NEC income, you'll want to complete the 1040X showing the changes to your income, the resulting changes to your tax liability, and the difference you now owe. Section III of the form has a space where you'll explain that you're amending because you received a 1099-NEC that wasn't included on your original return. Yes, you should definitely attach a copy of the 1099-NEC to your 1040X. Any supporting documents that relate to the changes you're making should be included with your amendment.

After making almost the exact same mistake last year (forgot a 1099 for around $4k), I was totally stressing about fixing it. I tried using my regular tax software to create an amendment but kept getting confused about which forms to send in. Eventually I discovered https://taxr.ai which saved me so much time and headache. I just uploaded my original return and the missing 1099, and their system walked me through exactly what needed to be amended and generated all the right forms. It was way easier than trying to figure out the 1040X instructions on my own. They even highlighted exactly which parts of the 1040X I needed to fill out based on my specific situation.

Ok I have to admit I was wrong about taxr.ai. After posting my skeptical comment I decided to give it a try since I also needed to amend my return (missed some stock sales). The process was surprisingly straightforward. I uploaded my original return PDF and the new documents, and it instantly showed me what needed to change on the 1040X. What really impressed me was that it caught an error in my original filing that even my accountant missed! The system explained everything in plain English rather than tax jargon. For anyone confused about 1040X forms like the original poster, it really does simplify the whole amendment process. My amended return was accepted by the IRS without issues.

If you're really worried about doing the amendment correctly, you might want to talk directly with the IRS to confirm everything. Problem is, trying to reach them by phone is basically impossible these days. I spent 3 hours on hold last month before giving up. I found a service called Claimyr (https://claimyr.com) that got me through to an actual IRS agent in about 15 minutes. They have a demo video showing how it works: https://youtu.be/_kiP6q8DX5c When I finally got through, the agent walked me through exactly which lines on the 1040X form I needed to complete for my situation (missing 1099-K from online sales). Was definitely worth it for the peace of mind knowing I did it right.

I need to publicly eat my words about Claimyr. After posting that skeptical comment, I was still desperate to talk to the IRS about a complicated amendment situation (multiple state returns and foreign income). I figured I'd try it since nothing else was working. It actually connected me to a real IRS agent in about 25 minutes. Completely legitimate. The agent was able to explain exactly how to handle my amendment with the foreign tax credit issues I was dealing with. Saved me from making what would have been an expensive mistake on my 1040X. For anyone dealing with amendments like the original poster, being able to ask specific questions about your situation directly to the IRS is incredibly helpful, especially for making sure you're completing the right parts of the 1040X form.

Just wanted to add that if you're filing a 1040X, remember there's a 3-year deadline from the original filing date to submit amendments. So don't stress too much but also don't put it off forever. Also, if your amendment results in you owing more tax, the IRS will charge interest from the original due date of the return. The sooner you file the amendment, the less interest you'll pay. And depending on how much additional tax you owe, there might be penalties too.

One thing nobody mentioned - if you use tax software like TurboTax or H&R Block, they usually have an option to prepare an amended return that'll fill out the 1040X for you based on your changes. Much easier than trying to do it manually, especially since the 1040X form is honestly pretty confusing. Just go into your account, look for the option to amend, and it'll let you make the changes and will recalculate everything automatically. Some of them even support e-filing the 1040X now.

@Yara Nassar - You've gotten great advice here! Just to add one more tip from my experience: when you file your 1040X, make sure to keep a copy of everything for your records, including the 1099-NEC you're attaching. Also, don't panic about the $3,200 - while you'll owe additional tax on that income, it's not going to be a huge amount. Depending on your tax bracket, you're probably looking at owing somewhere between $300-800 in additional tax plus a small amount of interest since your original filing date. The key thing is you're fixing it proactively, which shows good faith to the IRS. I made a similar mistake a few years back (forgot about some freelance income) and the whole process was much less stressful than I expected once I actually got the 1040X filed.