There really is no normal (or customary and usual) practice for these matters.
Legally, you are not required to do anything. In fact, some companies actually require that employees who have access to coverage through their spouses obtain their medical insurance coverage that way--versus using the insurance offered by their own employer.
Having said that, many employers do offer an offset to employees who either choose to buy their own health insurance coverage or who access health insurance coverage through their spouse's employer's coverage.
You may want to pay people who do what this employee is doing an amount equal to say 50 percent of what you would be paying for her coverage if she were to stay on the insurance that you offer.
But, again, this is just a suggested amount. You can do anything you wish--including doing nothing at all.
Question added to topic Human Resources • January 5, 2010
Should I reimburse my employees who deny their company-provided health benefits?
One of my employees is now going on her husband's health insurance plan. I had been paying 100 percent of her insurance. Do I reimburse her for the full cost of her benefits or only a percentage?
Penny is a seasoned human resources executive and consultant with over 25 years of diverse business experience in advising enterprise leaders on employment-related matters.