But wouldn't that only help for next year? OP already owes for this year's taxes, so isn't it too late to increase 401k contributions for the tax year that already ended?

You're totally right and I should have been clearer. For the current tax bill that's already calculated, increasing 401k won't help since those contributions had to be made during the calendar year. For the IRA though, you actually have until the tax filing deadline (usually April 15) to make contributions that count for the previous year. So while the 401k ship has sailed for last year, you can still make that IRA contribution up to the filing deadline and potentially benefit from the backdoor Roth strategy others mentioned. My bad for not being specific about the timing difference.

Does that work if you have a regular job too? I have W-2 employment but also make about $15k from a side hustle. Would that qualify?

What about if I mostly work from home but occasionally go to coffee shops to work? Would those miles count?

No, unfortunately trips to coffee shops to work generally don't count as business mileage since they're considered a personal choice rather than a business necessity. The miles that do count would be things like driving to meet a client, traveling to a location for a project, picking up supplies specifically for your business, or attending a conference related to your field. The key distinction is whether the travel is necessary for your business rather than a preference about where you do your regular work.

Wait really? I've been filing 1099-NEC income for 3 years and had no idea about this. Is there a minimum income requirement to qualify?

That's really smart! Should I also make photocopies or are pictures enough? And should I mail it from the post office or can I just drop it in a mailbox?

Pictures are generally enough if they're clear and show all the information, but if you want to be extra cautious, photocopies are good too. Personally, I just take clear photos of each page with my phone and save them in a dedicated folder. I strongly recommend going to the post office counter rather than using a dropbox, especially for tax documents. At the counter, you can get a stamped receipt with the tracking number. For something as important as your tax return, that extra confirmation is worth the few minutes in line.

This is actually correct! I work as a tax preparer and there should be an option to indicate you don't have last year's AGI. Which software are you using? I can tell you exactly where to look for this option.

How do you separate the value of the land from the building for depreciation purposes? I've always been confused about that part. My property tax statement doesn't break it down clearly.

Your property tax assessment should actually have this breakdown. Check your property tax statement or look up your property on your county assessor's website - most will show the land value separately from the improvements (building) value. If it's not clearly stated, a common method is to use the ratio that other similar properties in your area use. Your tax professional can help with this, or you can look at comparable properties with known land/building breakdowns.

This is a really good point. My rental in the high-tax suburb has appreciated WAY more than my rental in the low-tax area. After 5 years, the difference in appreciation has completely dwarfed any tax deduction differences.

I do have some substantial deductions - I own my home and have mortgage interest, plus I make regular charitable contributions. I also contribute the max to my 401k. Would all of these affect how I should fill out my W4? I'm not married and don't have kids, so I'm filing as single.

Yes, those substantial deductions are likely a big part of why you're getting such large refunds! The default withholding calculations don't account for itemized deductions like mortgage interest and charitable contributions. Your 401k contributions should already be excluded from your withholding calculations automatically since they're pre-tax, but the itemized deductions need to be handled separately on your W4. You should enter the approximate amount of your itemized deductions that exceed the standard deduction on line 4(b) of your W4. This will reduce your withholding to account for these deductions.

I tried that but found it confusing because you need to have so much info on hand - like exactly how much you've had withheld so far this year and projected income for different sources. It was accurate when I finally got through it, but took me like an hour to complete.