Obamacare customers in California will see average insurance premium rates rise by 4.2 percent next year, officials announced Thursday. That average encompasses a very wide range of actual rates that 10 insurance companies will offer on the state's Obamacare marketplace, which this year sold plans to 1.4 million people. But 87 percent of California Obamacare enrollees will see rate hikes of less than 8 percent, and 16 percent of them will see rate decreases. And because all but 10 percent of enrollees receive some kind of subsidy to offset their coverage costs, the rate increases in many cases will amount to just several dollars per month.