CHICAGO — If you plan to use the last of your 2011 sick days before the end of the year – even if you’re not really under the weather – you might not be alone.

Companies that track employee time off and other worker issues say sick-day use among those who aren’t sick is on the rise. From 2006 to 2010, the Workforce Institute at Kronos, a human resources policy group, found an 18 percent increase among workers who admitted to taking a sick day when they weren’t really sick. And a 2007 survey by human resources consultant CCH found that two-thirds of U.S. employees who called in sick at the last minute actually weren’t.

“That’s ‘fake’ sick time,” director Joyce Maroney said.

Fake sick time is something that many companies can’t afford, especially in a struggling economy, but the reasons employees have for faking it often go beyond just playing hooky.

Using sick days to tend to the needs of children and older relatives is increasing among workers whose employers do not allow sick leave for family care, staffing professionals say.

“It’s not always an illegitimate reason,” said Julie Tappero, president of West Sound Workforce, a West Coast staffing service. “There are plenty of legitimate reasons why employees take sick days.”

David Ossip, president and CEO of work force management consultant Dayforce, said increased sick-time use is the result of economic strain on the family. Where there may have been a stay-at-home parent before, now both parents are working.

“People need a sense of work-life balance,” he said. “And this is an outcome of that.”

CCH found in its 2007 survey that periods of calling in sick are greatest on Monday and Friday, around holidays such as Christmas and the Fourth of July, and also during flu and hay fever seasons.

To offset the pattern, both Ossip and Tappero suggested that companies be more receptive by increasing flex time and introducing options for telecommuting or shift-trading.

“The rule of thumb is about 9 of 10 people are trustworthy,” Ossip said.