CSS W4 vs my W4 options

[JJ-]

We will likely have way too many federal taxes withheld this year, on the order of $3.5k after accounting for the monthly child tax payments. I went to go into adjust my W4 based on the suggestion in MDM's spreadsheet ($~$18k for step 3 annual) and, noticing a couple of sub steps for box 3, I wanted to make sure I had this right.
In my W4 form, there's a:
3a) number of qualifying children X * $2,000
3b) number of other dependents Y * $500
3c) other tax credits $Z
3 total - no entry but calculated from 3a-3c.

So I think what I can do is stick $18k in box 3c and that sets all 3 total to $18k. Do I have that right?

[MDM]

Don't see a 3c on https://www.irs.gov/pub/irs-pdf/fw4.pdf, but anyway Employers use the amount on [line 3] as an annual reduction in the amount of withholding. 

I think you are asking if you can simply put $18K where it says "Add the amounts above and enter the total here" even if there are no "amounts above".  If so, the answer is "yes".

[JJ-]

I stuck it in there because it's just one paycheck. I did a bit more research and found that I could check the exempt box to also stop withholding for the rest of the year but still have FICA collected, but this one seemed a bit more interesting.


Payroll is run Wednesday so I'll update whether this works out.

[MDM]

I stuck it in there because it's just one paycheck. I did a bit more research and found that I could check the exempt box to also stop withholding for the rest of the year but still have FICA collected, but this one seemed a bit more interesting.

If you are eligible to claim exempt (do check your 2020 form 1040 line 24) then either that or the large enough line 3 amount should provide exactly the same result.  Here's hoping payroll gets it right. :)

[JJ-]

I stuck it in there because it's just one paycheck. I did a bit more research and found that I could check the exempt box to also stop withholding for the rest of the year but still have FICA collected, but this one seemed a bit more interesting.

If you are eligible to claim exempt (do check your 2020 form 1040 line 24) then either that or the large enough line 3 amount should provide exactly the same result.  Here's hoping payroll gets it right. :)

Line 24 has taxes due ($6k), credits were higher, but I assumed that for next year I would need to re do a W-4 if I did check exempt. I'll probably change this number again next year in Jan or so to default MFJ and make adjustments earlier in the year.

[MDM]

Line 24 has taxes due ($6k), credits were higher, but I assumed that for next year I would need to re do a W-4 if I did check exempt. I'll probably change this number again next year in Jan or so to default MFJ and make adjustments earlier in the year.

That assumption is correct, but technically you don't meet (line 24 > $0) the criteria to use "exempt".  Would the IRS come after you?  Probably not, but given the line 3 alternative....

Your plan for next year looks good.

[JJ-]

I am very unsurprised that the Line 3 value resulted in a total withholding a whopping $0.00. Thanks again @MDM