30 million people might owe the IRS more money next year. Are you one?

Those counting on a tax refund next spring may get a shock instead, warns the Internal Revenue Service.

One in five people — or up to 30 million taxpayers — may not have adequate withholdings for 2018, according to a report from the U.S. Government Accountability Office.

The IRS is encouraging everyone to do a “paycheck checkup” to make sure enough tax is being withheld, after changes took effect earlier this year.

This will give taxpayers time to increase payments, if necessary, before the end of the year to avoid owing taxes and possibly being charged a penalty.

It’s up to each taxpayer to make sure enough money is being withheld from their paycheck. Often first-time workers and those who change jobs can be surprised at tax time if workplaces don’t educate them on proper withholding.

“The idea is to check it. Don’t be surprised,” said Jamie Dent, a certified public accountant in Ocean Springs. For those taking taxable income from their retirement account and paying estimated taxes, “It may not be enough anymore,” he said.

The IRS Withholding Calculator will let people know, by answering a series of questions, if the correct amount is being withheld.

Those most likely to be affected are:

▪ A two-income family

▪ Working two or more jobs at the same time or only work part of the year

▪ Are self-employed

▪ Retirees with pension income

▪ Claim credits like the child tax credit

▪ Have dependents age 17 or older

▪ Itemized deductions in 2017

▪ Have high income or a complex tax return

▪ Have a large tax refund or tax bill for 2017

Those with higher incomes are more likely to have an issue, he said. For taxpayers who earn $60,000 to $70,000 and barely have enough expenses to itemize, “You’ll probably see a tax decrease,” he said.

In February, many people saw their taxes decrease when adjustments were made under the 2017 Tax Cuts and Jobs Act. The new tax laws increased the standard deduction, doubled the child tax credit, and eliminated personal deductions and certain deductions like property taxes and employee business expenses.

Dent said if the amount being withheld is inadequate, taxpayers should change their W-4 form, increasing withholding so it will be enough to cover the taxes by the end of December.

They’ll have to do it again at the start of 2019. The IRS said it is readying a new W-4 form to better align with changes in the tax law.

This story was originally published October 3, 2018 at 5:00 AM.