@tunapiano1 here is how it works:
AGI = $105,000 less standard deduction of $27,700 leaves taxable income of $77,300
the tax on $77,300 is $8,839
with 4 children under the age of 17, there is $8000 of tax credits.
the tax due would be $839.
If you are in the 12% tax bracket, that does not mean ALL your income is taxes at 12%. Only the 'taxable' income is taxed (so the part after the standard deduction) and then the first $22,000 is taxed at 10% and then the rest is taxed at 12%.
for the W-4, STEP 1 should reflect "married filing Joint" and STEP 3 should list 4 children / $8000. I suspect your 'income after pre-tax deductions' is really less than $105,000. are you subtracting contributions to 401ks, medical premiums, dependent care / FSA, or HSAs from that number? That will change the equation. Many forget to subtract their 'pre-tax deductions' when thinking about how much they earn.
If your 'income after pre-tax deductions' is less than $98,000, I would not expect there to be any withholdings. The tax on $98,000 is $7,999 and the tax credit of $8,000 would negate that.
