These are the premiums paid by either employee or employer (the sum of the two) to an insurance company: on average employees pay about 25% of any plan. Below, we plot the percent increases (click to enlarge).
While insurance increases have been trending downward, the worst year-on-year increase has been 13% for families and 15% for singles, both in 2002. The rate of increase has been declining, with a local peak in 2011 of 7.5% and 9.5% for singles and families, respectively. A flashback to the premium increasing heydays of 2000-2005.