@Opus 17
It would be nice if the IRS tool actually told you how to complete the W-4 form correctly but it only estimates the bottom line of the tax return based of the current rate of withholding on the current paycheck. It is pretty much a useless tool if you don't know what to do with that information.
Filling in the new W-4 is more complicated than it was in the past ... so sometimes using the info in pub 15-T is more help : https://www.irs.gov/pub/irs-pdf/p15t.pdf
