Deciding when to take Social Security benefits involves making a guess about how long you'll live. But you have to be smart about how you make that guess, and one common mistake can lead you to guess wrong in assessing your true life expectancy in retirement.

In this installment of our Social Security Q&A series, Dan Caplinger, The Motley Fool's director of investment planning, answers a question from a Fool reader who asks what the correct life-expectancy figures are for making a smart decision about taking Social Security benefits.

Dan notes that life expectancies for newborns are in their late 70s, leading some to conclude that waiting until age 70 to take benefits is a big mistake. But Dan notes that you have to look at life expectancies for those who are already 62, which are longer. Dan points to figures from the Social Security Administration putting the current life expectancy for those at early retirement age at around 82 years for men and almost 85 years for women. Dan concludes that for many, the not-so-obvious but essential change in determining life expectancy should lead you to reconsider waiting longer before taking benefits, especially when you consider survivors' benefits.

Have general questions about Social Security? Email them to, and they might be the subject of a future video!

Dan Caplinger has no position in any stocks mentioned, and neither does The Motley Fool. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.