Richard L. Kaplan of the University of Illinois has written a guide, published in the Journal of Retirement Planning, to help people decide when to start collecting Social Security benefits.

The guide covers a myriad of variables, including the implications of tapping early retirement benefits -- available at age 62 -- rather than waiting until full retirement age -- increasing to 67 for people born in 1960 or later.

One of the biggest mistakes people make is underestimating their life expectancy, which now averages about 77 years in the United States, up from 61 when Social Security was established in 1935, Kaplan said.

Claiming Social Security at age 62 nets a roughly 25 percent cut in benefits that extends for a lifetime, Kaplan said, trimming a monthly payment that would amount to $1,000 at full retirement age to $750.

Other factors to consider are age and health of surviving spouse, health insurance costs and whether the person plans to stay working.

While retirement benefits can be claimed as early as age 62, Medicare coverage doesn't begin until 65, leaving a potentially costly gap.