The underlying cost of health care for employer health plans may increase about 6.4% in 2009.

Consultants at Hewitt Associates Inc., Lincolnshire, Ill, have published that figure in an analysis of cost and performance figures for 400 large employers with 13 million health plan participants.

Between 2007 and 2008, health care costs increased 6%, the Hewitt consultants report.

Hewitt says the average cost of coverage will increase to $8,863 per employee, from $8,331 this year, with employees’ share of the costs increasing to $1,946, from $1,806.

Hewitt is estimating that cost increases will average 8% for health maintenance organization plans and 5.5% for preferred provider plans.