If you're among the people facing substantially higher health insurance premiums with a plan set up under the Affordable Care Act, there are some steps you can take to limit your increase.

You'll want to act quickly because this year's open enrollment period started November 1 and ends January 31. Here's what you can do.

Find out how much the premium increase is where you live. Premiums are going up a lot in Phoenix (145 percent), Birmingham (71 percent) and Philadelphia (51 percent). They're rising just a little in Los Angeles and Detroit (5 percent), and falling in Cleveland (down 2 percent) and Indianapolis (down 4 percent), according to an analysis by the Kaiser Family Foundation.

“Premiums reflect what insurers expect to pay for claims,” explains Lynn Quincy, director of Consumers Union's Healthcare Value Hub (Consumers Union is the policy and mobilization arm of Consumer Reports). “In a lot of states, insurers underestimated what they were going to be spending.”

That explains, in part, why prices are going up.

The Healthcare.gov website says that you should visit your state’s online health insurance marketplace to find out how prices are changing in your zip code. (If you’re not sure how to find your marketplace, go to Healthcare.gov and click on "Take the First Step to Apply" and follow the instructions.)

Look into whether you are eligible for a subsidy. About 85 percent of the people who buy insurance through their marketplaces get premium subsidies, according to the U.S. Department of Health and Human Services. These subsidies not only save them money, but also insulate them almost completely from any premium increases, no matter how large.

Your marketplace will walk you through the process of determining subsidy eligibility. Remember that you can only use your subsidy if you shop on the marketplace, according to the Kaiser Family Foundation. Off-marketplace plans don’t qualify for subsidies.

Also remember this: Of the approximately 7 million people who have bought insurance on their own outside of a marketplace, about 2.5 million are eligible for financial help with premiums but probably don’t know it, according to Health and Human Services. Another 5.3 million people would qualify for a subsidy but don't get it because they haven't signed up for insurance, according to a recent study by the Kaiser Family Foundation.

If you get a premium subsidy, work it. Your subsidy is calculated to cap your premium at a specified percentage of your income, based on the so-called benchmark Silver plan, according to the Kaiser Family Foundation study. It is the second-cheapest plan available to you.

The relative costs of Silver plans in your area may have changed since last open enrollment, so you can’t assume that the cheapest choice this year will still be the cheapest next year. But once you know the size of your subsidy, you can treat it like a gift certificate and apply it to any marketplace plan. You may find a Silver or Bronze plan that, with your subsidy, is actually cheaper than what you have now, says Health and Human Services.

Use the new marketplace shopping tools. Healthcare.gov has a valuable new feature this year that allows you to see your estimated total annual cost—premiums plus out of pocket expenses—based on whether you expect to be a high, medium, or low user of health services. If you have high health care expenses, you may find that that a plan with a higher premium offers lower overall total costs.

Also new this year on Healthcare.gov is a doctor and drug finder tool. You enter the names of drugs or doctors you want in your plan, and your search results will call out the plans that include them.

If you don’t get a subsidy, try to economize. Subsidies phase out if your household income for 2017 will be higher than $47,520 for an individual, $64,080 for a couple, or $97,200 for a family of four, according to calculations by the advocacy group, Families USA based on data from Health and Human Services. It’s this group of consumers who have no protection against big premium increases. 

Your choices may not be great, but there are steps you can take to lower your costs. Consider a plan with a smaller provider network. Because of the way insurance contracting works, these so-called “narrow network plans" are generally cheaper, explains Karen Pollitz, an insurance expert with the Kaiser Family Foundation. If your health care needs are uncomplicated, your provider is in that network, or you are willing to switch doctors and hospitals, they may be a reasonable choice.

Also, consider switching to a higher deductible plan. The premium will be lower, but, cautions Pollitz, “take a good look at your finances and ask yourself if you could come up with that $5,000 deductible if you had to.” Some marketplaces offer high-deductible plans that will cover three or four doctor office visits before you meet the deductible. And remember that all plans must cover 100 percent of specified preventive services regardless of whether you have met your deductible.