Unfortunately, we can't get state to zero, they object to claiming that many exemptions (which are worth less than federal exemptions were).
Does state law prevent claiming that many, or does a different phrase better describe the situation?
Hmm, not sure of the exact wording of state law on the subject, but 15 exemptions is the point at which you've simply gone too far. It's a long time since I originally researched this, so I'm fuzzy on precisely how they put it (absolutely cannot claim 15 or greater, or more of a massively ridiculous level of state scrutiny if attempting to claim 15 or greater). I do remember calculating that I'd need 25 to reach zero withholding at that time. Now I've got DH's state withholding to zero, since we've ramped up to max HSA, and max 401k + some catchup contributions, as these come out before tax withholding is figured. I have no option for either of those, and my part time work has bumped up enough to begin creeping above the zero withholding level with 10 exemptions. I'll just need to go all the way to 14.
First world problems. It's just stupid to have refundable credits, and arbitrary limits to adjusting for them effectively. It's obviously
possible to consistently be eligible for refundable credits exceeding tax liability, as we've used this strategy for years, first using the refunds to rapidly pay down our mortgage, and then later to fund Roth IRAs for both of us. They are shrinking as the kids leave the nest, but there's still opportunity until DS5 is no longer our dependent.