My lay understanding: We used to get deductions on taxable income for each kid. Trump's tax cut package changed that so it's now a tax credit but not a deduction on income.

Since the adjusted income is what Utah bases its calculations on, this means our income effectively increased by the amount of those deductions--a lot.

Rather than actually try and figure out what this would mean, the Utah legislature just reduced the tax rate from 5.00% to 4.95% and figured that it would all come out in the wash.

Of course, what that really means is that if you have no kids you get to enjoy the lower rate. If you make over $150,000 you get to enjoy the lower rate since you didn't get those deductions before. But if you make less than that and have kids, especially if you have a lot of them, that 0.05% tax cut doesn't come close to counteracting the much higher number Utah is now using for your income.

In other words, Utah's legislature didn't realize what effect Trump's tax cut would have on Utah's taxes, and as a result they have effectively given a small tax break to the wealthy and the childless and a big tax hike--per child--to everyone else.