Anybody know if net investment income is also subject to the additional Medicare tax? I'm in a similar MFS situation but also have some investment income.

Just wanted to add a practical tip for anyone dealing with this situation - if you know you're going to owe Additional Medicare Tax because of the withholding/threshold mismatch, consider making estimated tax payments throughout the year to avoid underpayment penalties. I learned this the hard way when I was MFS and earning around $160k. Even though my employer wasn't withholding the additional Medicare tax (since I was under $200k), I still owed it at the $125k threshold. The IRS hit me with an underpayment penalty because I didn't make quarterly payments to cover the gap. You can use Form 1040ES to calculate and make these payments online. It's much easier than dealing with a surprise tax bill and penalty in April.

Has anyone used both Guideline and Gusto for the retirement plan setup? I'm trying to figure out if having them integrated makes it easier to claim these Secure Act 2.0 credits or if it's basically the same no matter which provider you use.

I've been following this thread closely as I'm in a similar situation with my small consulting firm (6 employees, also S-Corp structure). Based on everyone's experiences here, it sounds like the key is making sure you have proper documentation of all setup costs and that your payroll provider can generate the right reports for Form 8881. One thing I'd add - if you're already using Gusto, they actually have some built-in retirement plan options that qualify for Secure Act 2.0 credits. You might want to check with them specifically about their 401(k) offerings rather than going with a separate provider. Sometimes having everything integrated makes the reporting cleaner come tax time. Also, since you mentioned being confused about the credits - the IRS actually published some updated guidance in late 2023 (Notice 2023-75) that clarifies a lot of the questions people have been asking in this thread. Worth checking out if you want the official details rather than relying on third-party interpretations.

Does anyone know if there are different GILTI rules for different industries? We're in software development with significant IP held offshore, and I'm not sure if there are specific provisions we need to be aware of.

I've been following this discussion with great interest as someone who's also navigating GILTI complexities. One thing I haven't seen mentioned yet is the impact of timing differences between U.S. and foreign tax years on GILTI calculations. Our family business has operations in the UK where the tax year ends in March, while our U.S. tax year is calendar year. This creates some tricky situations for calculating the foreign tax credits and determining which year's foreign taxes can be credited against which year's GILTI inclusion. Also, for those dealing with multiple foreign subsidiaries, don't forget about the tested loss rules. If one of your CFCs has a tested loss in the same tax year that another has tested income, the loss can reduce your overall GILTI inclusion. This can be particularly beneficial if you have operations in different stages of development or seasonal businesses. The recordkeeping requirements for GILTI are also pretty intense - you need to track basis in foreign subsidiaries, foreign tax payments, and depreciation schedules for tangible property on a CFC-by-CFC basis. I'd recommend getting your documentation systems set up properly from the start rather than trying to reconstruct everything later.

I've found that calling SBTPG right at 10am CT (when they open) gives you the best chance of shorter hold times. After 11am, you're looking at 45+ minute waits easily. Also, if you're an independent contractor like the original poster, you might want to check if your tax software offers any expedited refund tracking services - some of them have direct lines to SBTPG that can bypass the general customer service queue. Worth asking your tax preparer about it since you need the funds for quarterly payments.

As someone who's dealt with SBTPG delays multiple times, I'd recommend calling them at exactly 10am CT when they open - that's your best shot at getting through without a massive hold time. But honestly, three days isn't that unusual for them, especially during tax season. Since you're an independent contractor needing funds for quarterly payments, you might also want to check if your tax software (TurboTax, etc.) has a priority support line that can contact SBTPG on your behalf - sometimes they have backdoor channels that regular customers don't know about. Also worth logging into the SBTPG portal to screenshot your current status in case you need to reference specific details when you do get through to an agent.

Something else to consider - check if you have any other income that isn't having taxes withheld, like investments, side gigs, etc. My husband and I were in the same boat until we realized our investment income wasn't being factored into our withholding.

Another thing to consider is making quarterly estimated tax payments if your withholding still falls short after updating your W4s. Since you both got promotions mid-year, the withholding system might not have caught up to your new income levels quickly enough. You can calculate quarterly payments based on either 100% of last year's tax liability or 90% of this year's expected tax (110% if your AGI was over $150k). This gives you a safety net if your W4 adjustments aren't quite right, and you avoid underpayment penalties. The IRS Form 1040ES has worksheets to help calculate this, or you can make payments online through EFTPS. It's especially helpful for people with variable income or multiple income sources.