The study forecast that without intervention, premiums will rise by more than 60 percent between 2011 and 2020, bringing a family's average annual cost for coverage to $24,740 in less than 10 years.
"The rising share of premiums paid for by workers have been taking an ever greater cut out of paychecks, especially for those with family plans," study authors wrote. "At the same time, job-based insurance provides less financial protection: per-person deductibles more than doubled in most states over the eight-year period [2003-2011].
"The net result is that it is more difficult for many insured workers and their families to save for education or retirement — or simply to meet day-to-day living expenses."
The rising costs can be partly explained by "poorly coordinated care, duplicative services and administrative waste," as well as uneven pricing for medical services, Commonwealth said.
The group praised President Obama's signature healthcare reform law for expanding oversight of the insurance industry, mandating new market rules and encouraging better care since its passage in 2010.
But study authors warned that the U.S. healthcare system needs another overhaul before insurance prices will drop.
"Within the private insurance market, prices paid for care have been rising rapidly and vary widely for the same service across states, and often for the same providers, depending on the source of insurance," authors wrote.
"Across the country, evidence abounds of wasteful, duplicative, poorly coordinated, and, at times, unsafe care.
"Improvement in health system performance, with greater accountability for the total costs of care, will depend on policies that further the public interest by promoting better, more affordable care for all families, whether insured through employers, insurance exchanges or public programs."
The study added that debates over healthcare costs should focus more on trends in the private market, as spending per Medicare beneficiary is projected to increase at a slower rate over the next decade than spending on people insured through their employers.
Republican analysts used the study to blast Obama and his healthcare law.
"Candidate Obama promised repeatedly that his health plan would cut premiums — not merely 'slow the growth rate,' but CUT premiums in absolute terms — by an average of $2,500 per family within his first term," said Chris Jacobs, senior GOP policy analyst with Joint Economic Committee, in an email to reporters.
"A projected increase of 'only' $6,700 under Commonwealth’s best case scenario comes nowhere near close to meeting candidate Obama’s pledge to cut premiums by $2,500 — rather, it breaks that promise by nearly $10,000 per family."
He added, "Instead of holding campaign-style rallies in an attempt to raise taxes on job creators, President Obama could get to work on fulfilling his campaign pledge, and avoid socking middle-class families with tens of thousands of dollars in higher premium costs due to his unpopular law’s failure to deliver."