Thanks for the advice about documentation. I'm starting a spreadsheet now to track everything. Do you happen to know if I should respond to the specific address on the deficiency notice or is there a better department to contact directly?

Always respond to the exact address on the deficiency notice - that's crucial. It should go to the specific department handling your case. Make copies of everything you send, and I strongly recommend using certified mail with return receipt so you have proof of delivery. For extra protection, you might also want to fax the same documents (if a fax number is provided) and keep the confirmation page. The IRS operates in silos, so documentation sent to the wrong department might as well have never been sent at all.

Happened to my sister too! PayPal reported her entire transaction volume including money she was just transferring between her own accounts. The IRS tried to tax her on money that was literally just moving from one account to another. Such a broken system.

What about if one spouse is self-employed with a Schedule C business and the other is W-2? Does that change the calculation at all?

In a self-employed and W-2 earner situation, filing jointly is usually still more advantageous. The self-employed spouse can still take all their business deductions on Schedule C regardless of filing status. When filing jointly, you might actually benefit more from certain deductions like the Qualified Business Income deduction, which can be affected by your combined household income. One scenario where separate filing might help is if the self-employed spouse has potential audit concerns or inconsistent income reporting that could create tax issues. In that case, the W-2 earner might want to file separately to avoid joint liability. But strictly from a tax savings perspective, joint filing typically results in a lower total tax bill even with a Schedule C business involved.

I've used it and it works pretty well. Just make sure you have your most recent paystubs and last year's tax return handy when you use it. The calculator will tell you exactly what to put on your W-4s. My husband and I both earn around $65k and we had to add about $80 additional withholding per paycheck each to break even.

Does making those "good faith" payments actually work though? Like, do they really care about the effort or do they just calculate the penalties strictly by the numbers?

In my experience, making good faith payments absolutely helps. While the penalties are calculated mathematically, having a history of attempting to comply can help if you ever need to request penalty abatement. The IRS has a First Time Penalty Abatement policy that's easier to qualify for if you show a pattern of trying to comply. The other practical benefit is psychological - making regular smaller payments is much less painful than facing a huge tax bill plus penalties all at once. Even if you underpay somewhat each quarter, you're still reducing the base amount that penalties are calculated on, which saves money in the long run.

TurboTax Self-Employed can handle Form 2210, but it's not great at explaining the annualized income method. I used it last year and still ended up confused about whether I was doing it right. If your situation is straightforward it might be fine, but with variable income throughout the year, I'd recommend getting some help.

How far back can you go to fix this kind of mistake? My mom passed 3 years ago and I'm just now learning about step up basis.

You can generally file an amended return within 3 years from the date you filed your original return, or within 2 years from the date you paid the tax, whichever is later. So you're likely still within the window to fix it! If you sold inherited assets and used the original purchase price instead of the stepped-up basis, you definitely should file an amended return. The process isn't actually that difficult - just file Form 1040-X and include any schedules that change as a result of the correction.

What about for stuff like mutual funds? Do you use the NAV for the date of death?

Could you explain how to actually calculate this with an example? I'm trying to do this math myself but getting confused about where the bracket cutoffs are and how to determine the additional amount needed.

Sure! Let's use 2024 tax brackets for a single filer as an example. The 22% bracket goes from $44,726 to $95,375, and the 24% bracket is $95,376 to $182,100. If your first job pays $85,000, you're already in the 22% bracket. When you add $55,000 from the second job, your total is $140,000. So $95,375 - $85,000 = $10,375 of your second job income is still in the 22% bracket, and the remaining $44,625 is in the 24% bracket. The additional tax you'd owe is: $10,375 × 22% = $2,282.50, plus $44,625 × 24% = $10,710. Total extra tax of $12,992.50. If you're paid biweekly (26 paychecks), you'd need about $500 extra withheld per paycheck to cover this. You could either check the multiple jobs box on one W-4 or add an additional amount to Step 4(c).

I use it regularly and find it pretty accurate, but you definitely need your paystubs and last year's tax return handy. The key is entering the information exactly as requested. For the second job, you can enter the expected annual salary and $0 for withholding so far if you haven't started yet. The estimator will then tell you exactly what to put on each W-4. I've found it gets me within $100 of my actual tax bill every year.