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How to calculate full-time employees
You don’t have to insure your part-time workers—defined as less than 30 hours a week—but you do have to include them in calculating your number of full-time workers.
Here’s how: Take your total part-time hours in a month and divide by 120. Then add those “full-time equivalent employees” to your actual number of full-time employees.
Under most current insurance plans, workers can choose whether or not to join. But under Obamacare, all workers in large firms will be automatically enrolled, unless they opt out. That could mean paying premiums for many more workers than before.