As the window for correcting paycheck withholding errors starts to close, a new survey shows why more than half of respondents failed to update their withholding: They don’t know how.

Only 46 percent of respondents to the HR Block survey said they felt prepared to update their W-4 on their own, and many showed confusion over what information a W-4 uses, when and where to submit a W-4, and how allowances increase or decrease withholding.

“Consumers mostly want to get the same size refund as they have in prior years, while 47 percent actually expect a larger refund. But they haven’t taken action to make that happen,” Kathy Pickering with the Tax Institute at Block said in a statement.

Among the survey’s findings:

• Only 19 percent of respondents updated their paycheck withholding after tax reform. Another 40 percent said they updated their W-2 after tax reform (which cannot be done), and 17 percent said they updated their insurance documents. Nearly half (45 percent) of respondents were unsure what factors could be considered a withholding allowance on their W-4.
• Respondents were confused about who to submit an updated W-4 to: 42 percent knew it should go to their employer, but some thought it went to the IRS (27 percent), their financial advisor (7 percent) or the Social Security Administration (6 percent). In addition, 47 percent did not know they can update their W-4 at any time.
• Only 48 percent knew that increasing withholding would result in a larger refund, while 47 percent knew that decreasing withholding would result in larger paychecks.
• Only 46 percent felt prepared to update their W-4, while 31 percent did not have anyone they trusted to help.