I was double-checking my 2019 tax planning against my pay stub when I found out that I had a miscalculation months ago when adjusting things for a raise/bonus. At this point I've already overpaid my expected federal taxes, and have nearly overpaid expected state taxes.
So I redid the calculations, figured out the number of exemptions that would bring federal withholding to $0 and state withholding to the correct amount, and went into my employer's W-4 update system. At which point I found out that my state has a rule that if you're claiming 10 or more exemptions, you need to do a manual W-4 to submit to the state for them to verify. Which they won't be able to verify because the W-4 doesn't include state-specific credits that I qualify for.
Guess I'll be giving my state a no-interest loan for the foreseeable future.