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If you are starting a new job next year or if you want to adjust the amount of income tax withheld from your paycheck, the form that you will have to complete and give to your employer will look much different.

Form W-4, which instructs employers how much tax to withhold, got a makeover for 2020 from the IRS.

The redesign reflects changes to the federal tax code from the Tax Cuts and Jobs Act, which took effect last year.

The update, the IRS said, “reduces the form’s complexity and increases the transparency and accuracy of the withholding system.”

The new design may at first appear daunting, said Pete Isberg, vice president of government affairs with payroll processor ADP, but overall “it’s a lot more straightforward.”

Still, it’s a tax form. The American Payroll Association, an industry group, has warned employers that explaining the new form to workers may be “challenging” and has provided a sample letter to help guide employees.

First major redesign in decades

Accurate paycheck withholding is important because if too little money is deducted, you may face an unwelcome bill — and possibly a penalty — at tax time. Ideally, tax experts said, the amount withheld should roughly match the amount of tax owed.

If too much money is deducted, you may get a fat tax refund. Some people prefer large refunds as a sort of forced savings, said Alice Jacobsohn, senior manager of government relations with the payroll association. But a big refund means you gave the government a no-interest loan.

While the W-4 form had been tweaked over the years, the last major redesign occurred in 1987, in response to the Tax Reform Act of 1986. The old form was deemed too complex, so it was changed to cut down on work sheets and other instructions, an IRS spokesman, Eric Smith, said in an e-mail.

Perhaps the most obvious change is the banishment of “allowances,” which were used to calculate withholding on the previous W-4 form. The more allowances claimed, the less money the employer deducted for taxes.

But allowances were based on personal exemptions — an amount of money you could deduct for yourself and for each of your dependents — and those are now unavailable to taxpayers under the new tax law.

Instead, the new form takes workers through five steps that aim to account for all sources of income — including second jobs, a spouse’s job, self-employment income, and even income from things like dividends and interest — to determine the correct withholding amount.

Employees also enter information about dependents and tax deductions to fine-tune withholdings.

“It’s like a mini income tax return,” said Andy Phillips, director of H&R Block’s Tax Institute.

Some workers may be leery about alerting employers to second jobs or sharing details about investment income, said Kelley Long, a consumer financial education advocate with the American Institute of Certified Public Accountants.

To address those concerns, the form allows workers to use the IRS’ online tax withholding estimator tool or to complete a printed work sheet to determine how much to withhold.

The amount is entered on a separate “extra withholding” line, without details about how it was calculated. (Data from the estimator and the work sheet are not shared with the employer.)

Workers may also calculate the amount and then make separate, estimated tax payments to the IRS, independent of paycheck withholding.

May require extra time to complete

The withholding estimator asks detailed questions, so it’s helpful to have last year’s tax return handy along with your most recent pay stub.

Because new employees may not have the documents at work or may want to confer with a spouse, Isberg suggests that employers give new hires extra time to fill out the form — perhaps by letting them take it home.

Alternatively, if new employees are rushed for time, they can simply fill out the first step of the form — which asks for their name, address, Social Security number and filing status — and sign it (Step 5), Isberg said. Then, after reviewing their withholdings at their convenience, they can submit a revised form to make any necessary changes.

Isberg said employees should read the form’s instructions carefully to be sure they understood what information they were being asked to provide.

The IRS offers a series of questions and answers about the revisions. ADP also offers information on its website. And H&R Block offers a graphic comparing the new and old forms.

Ann Carrns writes for the New York Times.