A few things that jump out to me from your question. A child born anytime during the year is eligible for the child tax credit, so it is not a pro-rata amount based upon the date of birth. Only one of you should be claiming the child tax credits in Step 3 of the W-4, assuming your combined income is below $400,000, therefore, Step 3, assuming the other child is below the age of 17, should be $4,000.
With the birth of a child this year, one or both of you may work less during the year as well, so your overall income may be less as well. Step 2 should at a minimum have the Box checked in Step 2 for two jobs also.
The 529, assuming the state you live in allows a deduction or credit for a contribution, only impacts state tax withholding. If you took the standard deduction last year, it is likely you would be taking it in 2025 as well, since medical expenses as an itemized deduction are limited to 7.5% of adjusted gross income. An example of this would be if your adjusted gross income is $100,000 the first $7,500 of medical is not an itemized deduction.
Best of luck with what I hope is the healthy birth of your child @Kuddin2
All the best,
Marc T.
TurboTax Live Tax Expert
28 Years of Experience Helping Clients
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