Millions of Americans who bought individual health insurance outside the Affordable Care Act’s public exchanges could be leaving money on the table if they skip those marketplaces again in picking 2017 coverage, a new report says.

The Department of Health and Human Services estimates that 2.5 million people who bought so-called off-exchange coverage for this year might have income levels that qualify them for tax credits to help pay the premium.

These marketplaces offer tax credits to customers with income levels up to four times the federal poverty level, or nearly $100,000 for a family of four. The lower the income, the more help a customer receives. But in order to receive a subsidy, the customer must buy insurance through the exchanges.

HHS says several states have more than 100,000 people enrolled in off-exchange individual coverage who might qualify for help.

Those who buy individual coverage without tax credit help — an estimated 6.9 million people, according to the report — pay the full price of the policy. That can expose them to steep premium increases if they don’t switch to a cheaper plan. Insurers in some markets have asked for premium hikes of well over 10 percent for 2017.