In theory, the new withholding rate tables should take effect with your first paycheck in 2018. However, it could take some time before your employer and payroll companies like ADP and the like can update their software. Im sure they are working OT to get it done, but in my experience as a PR professional, dont be surprised if you dont see the new rate tables reflected in your paycheck right away.
What about the $500/dependent credit? Is is gone?
Personal exemptions are gone. Today you're allowed to claim a $4,050 personal exemption for yourself, your spouse and each of your dependents. Doing so lowers your taxable income and thus your tax burden. The GOP tax plan eliminates that option.
But the standard deduction doubles. For me as a single person, I win, Im not so sure about families with many children, however the child tax credit increases The credit would be doubled to $2,000 for children under 17. It also would be made available to high earners because the bill would raise the income threshold under which filers may claim the full credit to $200,000 for single parents, up from $75,000 today; and to $400,000 for married couples, up from $110,000 today.
This is a pretty good overview.
http://money.cnn.com/2017/12/15/news/economy/gop-tax-plan-details/index.html
They should make the availability unlimited, IMO, but this is a good start.
I am talking about the dependents not exemptions.