Understanding how 401k contributions impact my AGI - confused about multiple jobs calculation

You've got the right idea! Traditional 401k contributions are pre-tax and reduce your AGI. Since these contributions are made before taxes are calculated, they directly lower your Adjusted Gross Income. In your case, if your total gross income across all three jobs was $98,500 and you contributed $15,600 to a traditional 401k, your AGI would indeed be reduced to $82,900 (assuming no other adjustments). This is true regardless of which employer's 401k plan you used. The IRS doesn't care which employer's plan you contributed to - they only care about the total pre-tax contributions you made during the tax year (up to the annual limit, which is $23,000 for 2025 if you're under 50). Just make sure your W-2 from the part-time job correctly shows the 401k contributions in Box 12 with code D, which indicates they've already been excluded from the wages reported in Box 1.

I went through a similar situation last year with multiple W-2s and 401k contributions. I spent HOURS trying to figure out the calculations and kept second-guessing myself. I finally found this tool called taxr.ai (https://taxr.ai) that analyzed all my tax documents and explained exactly how my 401k contributions affected my AGI. It actually showed me that I had some additional pre-tax contributions I hadn't considered from my FSA account that lowered my AGI even more. Saved me from making a mistake on my return! It broke down exactly how each deduction was calculated and showed me where everything was reported on my W-2s.

Just wanted to update - I tried taxr.ai after asking about it and wow, it really cleared up my confusion about my retirement contributions! I uploaded my W-2s and 1099s, and it immediately highlighted that my SEP-IRA contributions would reduce my AGI but not my self-employment tax (which I didn't realize). It also flagged that one of my W-2s had a coding error in Box 12 that would have caused me to double-count some retirement contributions. Definitely saved me from a potential audit headache. The explanations were super clear and I finally understand how all these pieces fit together for someone with multiple income sources.

If you're having trouble getting confirmation about how your 401k contributions were reported or need clarification from the IRS directly, good luck trying to reach them by phone. I spent 3 weeks trying to get through to ask about my similar situation. Eventually I found this service called Claimyr (https://claimyr.com) that got me connected to an IRS agent in about 15 minutes when I had been failing for weeks. They have a video showing how it works here: https://youtu.be/_kiP6q8DX5c The IRS agent confirmed that my traditional 401k contributions across multiple employers all reduced my AGI and explained exactly how to verify this on my W-2s. Saved me tons of uncertainty and stress!

I need to apologize for my skeptical comment earlier. After struggling for almost 2 weeks trying to reach the IRS about a similar retirement contribution question, I broke down and tried Claimyr. I was connected to an IRS agent in about 20 minutes. The agent confirmed exactly what others said here - 401k contributions reduce your AGI regardless of which employer's plan you use, and I was able to verify that my W-2s were showing the correct amounts in Box 1 vs Box 12. They also helped me understand how the contribution limits work across multiple employers, which was super helpful. I'm genuinely shocked at how well it worked after all my failed attempts to reach someone on my own. Definitely worth it for peace of mind on complicated tax situations.

Just to add some clarification about Box 1 vs Box 5 on your W-2s - Box 1 shows your taxable wages (after pre-tax deductions like 401k), while Box 5 shows your Medicare wages which generally includes your 401k contributions. So if you're trying to double-check that your 401k contributions were properly deducted from your AGI, you can often verify by comparing Box 1 and Box 5. The difference should include your 401k contributions (along with any other pre-tax deductions like health insurance).

Has anyone actually had issues with contributing to a 401k through a part-time job? My main employer doesn't offer a 401k but my weekend gig does, and I'm wondering if there's anything special I need to know.

Great question about contributing through a part-time job! I've been in a similar situation where my main employer didn't offer a 401k but my side job did. Tax-wise, it actually works exactly the same as if you contributed through your main job - the pre-tax contributions reduce your AGI dollar for dollar regardless of which employer's plan you use. The only real difference is that your W-2 from the part-time job will show the reduced wages in Box 1, while your main job's W-2 won't have any 401k deductions. When you file your taxes, the software just adds up all your Box 1 amounts from every W-2, so the AGI reduction happens automatically. One thing to be aware of is that if your part-time job has lower wages, you might not be able to contribute as much as you want (since contributions can't exceed your wages from that specific job). But it sounds like that's not an issue for you since you were able to contribute $15,600!