Social Security's cost-of-living adjustment could rise 2.7%. But Medicare Part B premiums are set to rise even more, eating most of the COLA.

Regardless of which of these is right, however, the COLA is about to buck a 29-year trend. That's because, for the first time since 1996, the COLA is going to be above 2.5% for five consecutive years. This is a once-in-a-generation shift for today's retirees, and it is not something that most people will probably see again in their lifetime.