To most people, it seems obvious that it's smart to wait as long as possible before applying for Social Security. But is this really the best thing to do? The answer is often no.

Central to this conclusion is the fact that the age at which you begin receiving benefits impacts the size of your monthly checks.

If you receive them at the earliest possible time -- the month after your 62nd birthday -- then your monthly benefits will be 25% lower than they would have been had you waited until full retirement at 66.

On the flip side, if you wait until turning 70, your benefits will be 32% greater than if you had started taking them at 66, or full retirement, and 76% larger had you elected early retirement at 62.

As Motley Fool contributor John Maxfield discusses in the video below, however, these comparisons ignore probably the most important variable: the lifespan of the average American. Once you factor this in, it becomes obvious that only a minority of people should wait until 70 to apply for benefits.

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