I'm not a CPA, so take this as you will, but I'm 97% sure there is no penalty for underpayment of estimated taxes. Technically you could pay $0 tax all year, but as long as you pay all the taxes you owe by April 15th the following year (I believe that's the due date for filing your taxes) you will not be penalized.
I'm no CPA either, and won't even pretend to understand the deeper arcana of the U.S. tax code. That said, our CPA has warned us in recent years that we are in danger of having to pay such an "underpayment" penalty, because the nature and amount of our income is such that we need to have additional income withheld on our W-4s (i.e. specifying "0 allowances" isn't enough). The IRS spells out the details
here, but my understanding is that, in most cases, you're expected to pay at least 90% of your tax liability over the course of the year through payroll withholding or quarterly estimated-tax payments.
I imagine that most people who reduce their withholding and qualify to take the EV credit in the same year will have no problem avoiding the penalty. The main reason I brought this question up was to raise awareness (and seek clarification) on scenarios like the following:
(1) Taxpayer reduces withholding by more than $7500, slips under 90% threshold, incurs penalty
(2) Taxpayer reduces withholding by $7500 in anticipation of the full credit, but only receives the $3750 credit, causing them to slip under the 90% threshold and incur the penalty
(3) Taxpayer reduces withholding by $7500, has an estimated delivery date in December, but the actual delivery date slips into January, so they cannot claim the EV credit for the year in which they reduced their withholding, causing them to fall beneath the 90% threshold and incur the penalty.
Of these three, scenario 3 seems like the most likely to occur, and also carries the greatest downside risk inasmuch as it makes a $7500 difference in expected vs. actual liability.
Are these legitimate concerns for someone who is considering reducing their paycheck withholding? Or have I flopped out of my tiny, non-CPA pond?