hello Lbryant:
pleased to help you. the best solution to this is use our tax estimator, it will give you a projection of what your tax liability or refund will be for the year, you can adjust income amounts and deductions, as you see fit. you will need a current pay stub with ytd income and ytd withholdings and then you can project out increase of income and withholdings.
https://turbotax.intuit.com/tax-tools/calculators/w4/ it is fairly easy to use.
may i also suggest our taxcaster calculator to project refund/tax due for the year.
https://turbotax.intuit.com/tax-tools/
should you still have questions after completing the calculators. we are open 5 am- 5 pm pacific daily , monday - friday and if you have the live feature with turbo tax feel free to call in and an agent like myself will be glad to help you.
hope this helps.