Hillary Clinton wantsAmericans to have access to Medicare starting at age 50. It's an ideawell worth considering, not least because so many Americans aged 50to 64 who don't have job-based health insurance struggle to affordthe relatively high premiums they're charged for private plans. AndMedicare is a popular, battle-tested and relativelyinexpensive insurance system, costing less per person than privateinsurance.

Such an expansion would have to be carefully designed, however,to make sure Medicare premiums for this age group accurately andtransparently reflect the cost of coverage. Underpricing wouldundercut private insurers competing for the same customers, andalso saddle taxpayers with the extra cost.

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The most straightforward approach would be to offer peopleyounger than 65 a price equal to the full cost of their coverage.That would probably be at least $7,600 for people in their early 60s -- anestimate the Congressional Budget Office came up with in 2008.Today, the figure would be even higher, and it's not clear how manypeople would want to pay it.

In contrast, the average second-most-generous Obamacare planthis year costs $10,911 for a 60-year-old. But thegovernment subsidizes those premiums through a tax credit to peoplewhose incomes are less than 400 percent of the poverty line. Itwould make sense to offer the same subsidies to people who wouldbuy into Medicare.

If the price were well calculated, a Medicare option could offerneeded competition in places where few companies sell insurance onstate exchanges. That's increasingly important: The number ofcounties where just one plan is available is projected to tripleto more than 650 next year. And coveringpreventive care for people during the decade before they reach 65could potentially lower Medicare spending on chronicdiseases.

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Selling Medicare policies on the exchanges would be anambitious, yet not radical, way to expand insurance coverage. Inother words, just the kind of incremental reform the health-caresystem needs.

To contact the senior editor responsible for Bloomberg View’seditorials: David Shipley at [email protected].

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