W-4

I am trying to help my kids figure out their tax withholding for 2024 so they don't have to pay taxes next April.  I worked through both the IRS and the TurboTax tools, and they are miles apart! The IRS tool says they're going to be short $1,094, and the TurboTax tool says they'll be short over $4,000!! I used all the same information on both. How do I know which one is correct? Why is this form so #$@* complicated! Can someone please help me?

Thank you,

Lisa