The IRS and the Treasury, however, said on Thursday that new withholding tables work with W-4 forms already filed with employers.
As a result, Americans are being encouraged to check their payroll using the IRS online calculator, which will not be available until next month, to make sure that they are not overpaying or underpaying their taxes.
The tax law is projected to add between $1 trillion to $1.5 trillion to the debt over 10 years because of a fall in revenue, something Democrats have decried but Republicans have said will help spur economic growth.
"We estimate that 90 percent of wage earners will experience an increase in their take home pay", said U.S. Treasury Secretary Steven T. Mnuchin.
Democrats remain critical of the Republican-led tax bill and warn that the the new tax guidelines allow the Trump administration to deliver on the promise of a large middle-class tax cut ahead of the 2018 mid-term elections, but, in fact, will leave taxpayers owing inordinately larger tax bills in 2019.
Another reason additional funds are needed is that although the tax bill was originally promoted as a simplification of the code, new complications have been added in some cases, including exemptions for most refinancings of home mortgages and loans closed after December 15 that had prior binding purchase contracts.
The new guidance will allow many taxpayers to start seeing bigger paychecks due to the new law.
Two aids of RJD chief Lalu serving him in jail - media reports
He further said, "This shows that Lalu commitment to social justice is a shame and he cares only for himself and his family members".
Americans will not be asked to input personal information into this online calculator, such as their names or Social Security Numbers, but they will need to input their income levels, family status, and a number of other details. Ron Wyden (D-Ore.) and Rep. Richard Neal (D-Mass.).
Many Americans are likely to see changes and adjustments this year in their tax payments as the law goes into effect. There are significant limitations on long-cherished deductions, such as the federal deduction for state income, property and sales taxes.
Nonpartisan tax experts project that the law will bring lower taxes for the great majority of Americans, though not all. California, New York and New Jersey are among the states that have been considering changes to their tax codes to blunt the pain that their residents could feel from the scaling back of the state and local tax deduction in the new law. Washington is encouraging employers to implement the new withholding tables as soon as possible, but no later than February 15. In the meantime, employers and payroll service providers should continue to use the existing 2017 withholding tables and systems.
And roughly three-quarters of tax filers are overwithheld because they take too few allowances.
The current tax withholding system is based on personal exemptions, which, under the new bill, was repealed.
"I think it's one of the more ridiculous comments to think you can take a real estate tax that you're required to make and dress that up as a charitable contribution", Mr. Mnuchin said.