One of President Obama's regular attacks on Paul Ryan's Medicare reform is that it would force seniors to pay $6,400 a year more for health care. But merely because he keeps repeating this doesn't mean it's in the same area code of accurate.

The claim is based on a now out-of-date Congressional Budget Office estimate of the gap between the cost of health care a decade from now, in 2022, and the size of the House budget's premium-support subsidy for a typical 65-year-old in 2022.

In...