The study looked at premiums for non-smoking 21-year-olds, 40-year-olds and 60-year-olds in each of the 11 states and the District of Columbia.
It compared four levels of plans available under Obama's law: bronze, silver, gold and platinum. Bronze plans will cover 60 percent of expected medical costs; silver plans will cover 70 percent; gold will cover 80 percent, and platinum 90 percent.
All plans cover the same benefits, but bronze features the lowest premiums, paired with higher deductibles and copays. Platinum plans would have the lowest out-of-pocket costs and the highest premiums.
Mid-range silver plans are considered the benchmark, because the tax credits will be keyed to the cost of the second-lowest-cost silver plan in a local area.
The average premium for a silver plan ranged from a low of $203 a month for a 21-year-old in Maryland to a high of $764 for a 60-year-old in Connecticut.
The silver plan premiums for 40-year-olds were roughly $75 a month higher than for 21-year-olds across the states. But the price jumped for 60-year-olds. The health law allows insurers to charge older adults up to three times more than younger ones. That's less of a spread than in most states now, but it could still be a shock.
"It's striking that the curve increases quite dramatically above age 40," said Pearson. "As you get older and approach Medicare age, your expected health costs start to rise pretty quickly."
But older consumers could also be the biggest beneficiaries of the tax credits, because they work by limiting what you pay for health insurance to a given percentage of your income.
For example, an individual making $23,000 would pay no more than 6.3 percent of their annual income — $1,450 — for a benchmark silver plan.
That help tapers off for those with solid middle-class incomes, above $30,000 for an individual and $60,000 for a family of four.
The study also found some striking price differences within certain states, generally larger ones. In New York, with 16 insurers participating, the difference between the cheapest and priciest silver premium was $418.