Thanks for breaking it down! So if I understand correctly, my $86k W2 would allow for: $23k employee contribution, then 25% of $86k = $21.5k employer contribution, which leaves $24.5k that I could contribute as after-tax dollars for immediate Roth conversion. So I could do the full MBDR, just not the full $69k as after-tax contributions. Is that right?

You've got it exactly right. With your $86k W2 salary, you can make the $23k employee deferral and about $21.5k as the employer contribution. That leaves approximately $24.5k that you can contribute as after-tax dollars for the Mega Backdoor Roth conversion. So while you can reach the full $69k overall limit, only a portion of that would be after-tax contributions eligible for the Roth conversion. This is still a fantastic strategy for building tax-free growth in your retirement savings, and your income level is absolutely sufficient to take advantage of it.

Did you have any issues with timing? I'm worried about setting up the solo 401k, making contributions, AND doing the Roth conversion all before the tax year ends. How tight is that timeline?

Their regular support is useless for this, but I paid extra for TurboTax Live last year and got connected with a CPA who actually knew about RSUs. She walked me through exactly where to make the adjustments in the software. Worth the upgrade if you're dealing with this regularly. She also helped me create a spreadsheet to track my RSU basis for future years, which has saved me tons of time.

Thanks for the tip about TurboTax Live! I'll give that a try. I've been thinking about switching to a CPA but they're so expensive in my area. A middle ground like this might be perfect.

This is super helpful - thank you! I just checked and my 1099-B does have that box checked. I'll make sure to use the adjustment code when I'm fixing this in TurboTax. Is this something that the IRS commonly flags? I'm worried about getting some kind of automated notice even if I do everything correctly.

It is something the IRS automated system flags if you don't handle it correctly, which is why using the proper adjustment code is important. Their matching system will compare your 1099-B to what you report, and if you don't explain the discrepancy properly, it can trigger a notice. But if you use code B on Form 8949 and include the explanation statement that TurboTax generates, you should be fine. I've been reporting RSUs this way for 5 years and never had an issue. The key is making sure you have documentation of your cost basis (like that supplemental tax form from your brokerage) in case you ever need to prove it.

But what if their parents added them as an authorized user on their HSA? Couldn't they contribute that way since it's still part of the family limit?

Being an authorized user on someone else's HSA is different from having your own HSA eligibility. Authorized users can withdraw funds from someone else's HSA for qualified medical expenses, but they don't gain contribution rights. HSA contribution eligibility is tied to having your own HDHP coverage. Being covered as a dependent on someone else's family plan doesn't make you eligible to contribute to any HSA, either yours or theirs. The family contribution limit belongs to the HSA account owner (the parents in this case), not to the dependents covered under their plan.

You've got the testing period concept right but the year wrong. The "last-month rule" would only help for 2023 contributions if OP had their own HSA-eligible coverage by December 1, 2023 (which they didn't). Since they only got their own HDHP coverage in January 2024, the last-month rule might apply to their 2024 contributions (if they maintain coverage through Dec 31, 2024), but it can't retroactively create eligibility for 2023.

Thanks, this is really interesting! I hadn't heard of the Series LLC before. Is this available in most states? And would each owner still get a K-1 showing their specific income after their individual expenses?

Series LLCs are currently available in about 20 states including Delaware, Texas, Illinois, and Nevada (among others), but the laws vary significantly by state. Even if your state doesn't allow them, you can form one in a state like Delaware and register it as a foreign entity in your home state, though this adds some complexity. Each owner would still receive a K-1 reflecting their share of income based on the operating agreement terms. The operating agreement would specify how individual expenses are accounted for before calculating each person's distributive share. This approach gives you the liability benefits of separate entities with the administrative simplicity of a single filing.

I wouldn't recommend a general partnership for this scenario. Without the LLC structure, all partners have unlimited personal liability for business debts and legal issues. That's a huge risk with 10 different people involved who all have separate business activities! An LLC provides crucial liability protection that a plain partnership doesn't.

Did you find any deductions or credits you were missing when you switched? My biggest fear is leaving money on the table by doing it myself.

I actually discovered I qualified for the Saver's Credit that my tax preparer had missed the previous two years! It's for retirement contributions if you're under certain income limits. FreeTaxUSA has a good review system that checks for credits you might qualify for based on your inputs. It asks questions throughout that help identify potential deductions. In my experience, it was actually more thorough than my preparer who was rushing through multiple clients' returns during tax season.

I've used both. TurboTax has a slicker interface but FreeTaxUSA is MUCH cheaper and does everything you need. TurboTax charges extra for homeowner stuff and childcare credits (they put it in their "Deluxe" tier). With FreeTaxUSA all those forms are included in the free federal filing. For your situation, you'd probably end up paying $120+ with TurboTax vs. about $25 total with FreeTaxUSA (free federal + state fee). The questions and guidance are very similar between them.