The Internal Revenue Services offices in Washington, D.C. Adam Jeffery | CNBC

Fine-tuning your tax withholding is about to get a little more complicated. The Internal Revenue Service is expected to release a draft of its new Form W-4, the form employees use to adjust the amount of income tax withheld from their pay, by the end of May. The draft form, which is expected to be in use for 2020, will be open for comments from the public. It will more closely reflect the changes from the Tax Cuts and Jobs Act. This overhaul of the tax law nearly doubled the standard deduction, eliminated personal exemptions and placed limits on certain itemized deductions. Last year, the Treasury Department and the IRS updated the withholding tables, incorporating these changes. Workers can anticipate putting in a little more time and effort to fill out the new form, said Pete Isberg, head of government relations at payroll company ADP. "If you want to get the withholding right, it will work like the tax return itself," he said. "There will be input areas that look more like a 1040 summary than the old Form W-4."

Get your tax return

"To get it right, you have to have your last year's tax return," said Isberg. He anticipates that in order to fill out the new W-4, employees will need to know their total deductions from the prior year, the tax credits they can expect to claim in the upcoming year, as well as additional sources of household income — including their spouse's earnings. "People don't generally remember their total deductions off the top of their head, so it's not going to be super easy to do," Isberg said. "But it's going to be more accurate." In general, tax withholding is a balancing act for filers.

If you want to get the withholding right, it will work like the tax return itself. Pete Isberg head of government relations at ADP

If you withhold far too much, you get a large refund the following year. But you've also given the government an interest-free loan. Withhold too little, and you take home more cash in your paycheck. But you may owe the IRS next spring. This year marked the first time filers submitted returns under the new tax law, and some wound up with smaller-than-expected refunds. Others owed the tax man. "They got more money in their pockets during the year, and they received smaller refunds," said David Desmarais, CPA and member of the American Institute of CPAs' personal financial planning executive committee. In all, the IRS issued 101.6 million refunds as of May 10, down about 1% from last year. The average refund check was $2,729, down from $2,778 last year, according to the IRS.

Prep for 2019

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