Chicago workers can expect to pay 12.4 percent more in health insurance premiums and out of pocket costs next year, according to a report from Lincolnshire-based Hewitt Associates.

The average employee cost, including premiums and out-of-pocket costs such as co-pays and co-insurance, will rise to $4,520 from $4,022 last year, the company said. That includes $2,286 in premiums and $2,234 for out-of-pocket costs.

For Chicago employers, the average cost per worker will rise 8.7 percent to $9,791, including employee contributions to premiums. That’s the highest increase since a 9.7 percent rise in 2006. Nationally, costs are expected to rise 8.8 percent next year.

Among factors driving the higher costs, employers are seeing an increase in the amount of charges and frequency of catastrophic claims as slower hiring has left employers with older workforces more prone to costly medical conditions, the human resources consulting and outsourcing company said.

Hewitt also estimates that health care reform requirements that dependents be covered to age 26 and the elimination of certain lifetime and annual limits contributed 1 percent to 2 percent of the increase. Most of the positive effects of the reform law won’t be felt for a few years, according to Ken Sperling, Hewitt’s health care practice leader.

Employers are responding to rising costs with plans to continue passing more of those costs along to workers over the next three to five years. Workers may see employers shifting plan designs from fixed dollar co-payments to co-insurance models, where employees pay a percentage of the out-of-pocket costs for each health care service, Hewitt said. Workers may also see higher deductibles, out-of-pocket-limits and cost sharing for use of non-network providers, Hewitt said.