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Can I make a single Q4 estimated tax payment of $10,000 to cover the shortfall and still avoid penalties?
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Does the fact that a large portion of my income was earned in Q4 allow this even though earlier quarters were $0?
As to taxable income, the default is that 1/4 is deemed earned in each period. You can use the annialized income installment method (AIIM) for all periods if that reduces the underpayment of estimated tax penalty.
see page 3 of the 2210. https://www.irs.gov/pub/irs-pdf/f2210.pdf
As to withholding, the default is 1/4 is deemed paid each period. You are allowed to use actual for each period.
As for estimates, they only count for the period for which they are deemed paid, which generally means they must be paid no later than the 15th of the month following the close of the period (the periods end on 3/31, 5/31, 8/31 and 12/31)
So the answer to your question is yes (or maybe - see below), but you must use the AIIM
I suggest using the 2210 (it's for 2024, but the 2025 form should be the same, except the years will be different) to see where you stand. Perhaps you can reduce or eliminate that estimate. Essentially, withholding and timely estimated tax payments must total 22.5% of your 2025 taxes for the first period, 45% for the second, 67.5% for the third, and 90% for the fourth. Note that the estimate must be paid by 1/15/2026, to count and then it only counts in the 4th period.
