Box 12 on W2 showing blank but I definitely contributed to 401k

This is definitely something that needs attention. Your 401(k) contributions should be reported in Box 12 with code D. This indicates your elective deferrals to a 401(k) plan, and it's important for various tax calculations and limits. It sounds like your employer made a mistake on your W-2. Since you can verify the contributions on your paystubs, you have evidence that the contributions were made. I would recommend contacting your payroll or HR department as soon as possible to request a corrected W-2 (which would be a W-2c). Don't file your taxes with the incorrect W-2, as this could potentially cause problems down the road, especially regarding retirement contribution limits and potentially even Social Security calculations.

After facing a similar issue last year, I found an amazing tool that helped me sort it out. I used https://taxr.ai to analyze my W-2 and paystubs, and it immediately flagged the discrepancy. The tool actually explained that my employer had incorrectly coded my retirement contributions and showed me exactly what needed to be fixed. What I really appreciated was how it walked me through the exact language to use when contacting HR, and even generated a template email I could send. Made the whole process so much less stressful since I felt like I knew exactly what I was talking about rather than fumbling through tax codes.

Just wanted to follow up! I tried https://taxr.ai after seeing it mentioned here, and wow - it immediately identified that my employer had incorrectly reported my health insurance premiums. The tool actually showed me that my premiums were being deducted pre-tax but weren't properly coded on my W-2. What I found super helpful was the document it generated for me to take to HR - it cited the exact tax codes and explained the issue in terms my HR department understood. They issued a corrected W-2c within a week! Definitely saved me a lot of headache and potentially having to amend my return later.

If you're having trouble getting your employer to fix this W-2 issue, I was in the same boat last year. After weeks of my HR giving me the runaround about my missing 401k contributions on Box 12, I found https://claimyr.com which got me through to an actual IRS agent in about 15 minutes. You can see how it works here: https://youtu.be/_kiP6q8DX5c The IRS agent walked me through exactly what forms my employer needed to file to correct the W-2 and even contacted my employer directly. Completely changed my view on dealing with the IRS - they were actually super helpful once I could actually talk to someone!

I need to eat some humble pie here. After posting my skeptical comment, I decided to try https://claimyr.com anyway because I was desperate to resolve an issue with my tax transcript. I was absolutely shocked when I got a call back in about 20 minutes connecting me to an actual IRS agent! The agent was able to help me figure out why my refund was delayed (there was a discrepancy with my reported retirement contributions, ironically similar to OP's issue). They also told me exactly what documentation I needed to provide to fix it. I would have been waiting months for a letter otherwise. Can't believe I wasted so many hours trying to call them myself.

Just FYI - sometimes the 401k contributions show up differently depending on the type of plan. My company has a "Safe Harbor" 401k and the employer matching contributions show up in box 12 with code S instead of D. Maybe check if your company has a special type of 401k plan? But your personal contributions should definitely be there with code D.

Could it be that you have a Roth 401k instead of a traditional one? Roth 401k contributions are still reported in Box 12 but with code AA instead of D. Might be worth checking what type of 401k you have.

I had a similar issue last year where my Box 12 was completely blank despite making 401k contributions all year. In my case, it turned out that our payroll system had a glitch that affected about 20 employees out of 200+ at my company. What helped me was gathering all my paystubs from the entire year and creating a simple spreadsheet showing the 401k deductions from each pay period. When I presented this to HR along with my account statement from our 401k provider (showing the actual deposits), they were able to quickly identify the error and issue a corrected W-2c within about 10 days. One thing to check - log into your actual 401k account and verify that all your contributions actually made it into the account. In rare cases, there can be issues where money is deducted but not properly transferred to the retirement plan provider. If the money is there, it's just a reporting error. If it's not, that's a much bigger problem that needs immediate attention.