KEY POINTS
  • The classic notion of retirement planning is a measure of savings and time.
  • "Longevity" planning is a more complete framework, said Joseph Coughlin, director of the MIT AgeLab.
  • Americans overlook many important aspects of old age. They include transportation, social life and small tasks that may be difficult or impossible. Many of them carry a financial cost.

The following is an excerpt from "This week, your wallet," a weekly audio show on Twitter produced by CNBC's Personal Finance team. Listen to the latest episode here.

 Americans are living longer — and it's changing the nature of retirement planning.