The IRS is encouraging taxpayers to review their tax withholding status as the 2017 tax year approaches its end.

Not doing so could affect your tax refund and result in an unexpected bill and an additional penalty next year, the agency said in a news release.

"The withholding review takes on even more importance given a tax law change that started last year. This change requires the IRS to hold refunds a few weeks for some early filers claiming the Earned Income Tax Credit and the Additional Child Tax Credit," the Internal Revenue Service said.

People with a second job especially need to check they are paying the right amount of taxes this year, the IRS said.

The IRS said employees should file a new Form W-4, Employee’s Withholding Allowance Certificate, with their employer before it gets too late in the year.

IRS.gov offers online help to make sure taxpayers aren't overpaying or underpaying taxes:


IRS Withholding Calculator – Online tool helps determine the correct amount of tax to withhold.
IRS Publication 505 – Tax Withholding and Estimated Tax.
Tax Withholding – Complete information on withholding, estimated taxes, FAQs and more.

Self-employed taxpayers can use the Form 1040-ES worksheet to figure their estimated tax payments.

Due to a December 2015 law, the IRS says it cannot issue refunds on tax returns claiming the Earned Income Tax Credit or the Additional Child Tax Credit before mid-February. The IRS said it must hold the entire refund.

This law change that took effect in 2017 helps ensure that taxpayers get the refund they are owed by giving the IRS more time to help detect and prevent fraud.

The IRS noted it and state tax agencies are improving protections against identity theft and refund fraud, which also could result in tax returns being delayed.

"How much you choose to withhold is a personal choice, but checking now can reduce the chance for a surprise tax bill when you file in 2018," said IRS Commissioner John Koskinen.