Many Americans who buy life insurance do so largely as part of their retirement planning.

That's according to new research from Northwestern Mutual Life Insurance Co. based in Milwaukee.

Its recent study found that one in four Americans over the age of 18 who bought life insurance cited retirement planning as their top reason.

"Individuals have long recognized the importance of life insurance in terms of providing financial protection to loved ones in the event of their death," says David Simbro, senior vice president of life and annuity products at Northwestern Mutual, in a press release about the survey. "However, the new study results show that people of all ages are also leveraging the flexibility of permanent life insurance to help meet long-term financial goals."

Trend expected to continue

Simbro expects life insurance to continue play a crucial role in planning, particularly as people grapple with the challenges of living longer in retirement.

Of those surveyed, 25 percent say that having enough money to live in retirement is what gives them the greatest peace of mind.

The poll also found that the older you are, the more likely retirement planning is your primary reason for buying life insurance. Thirty-one percent of those citing retirement planning as their primary reason are 55 or older while 25 percent are between the ages of 45 and 54, and 19 percent are 44 and under.

Other reasons for buying life insurance

Other reasons for buying life insurance that were cited by respondents include:

  • Marriage (32 percent)
  • Birth of a child (22 percent)
  • Home ownership (19 percent)
  • Leave an inheritance to heirs or charity (10 percent of those 18 to 34 and 2 percent of those 35-44).

Generational differences dictate how much to buy

The poll also found that generations calculate how much life insurance to buy differently:

  • Those 18-34 years old are more likely to factor in education expenses than those 45 and older.
  • More than a third of those 35 to 44 (38 percent) consider income replacement.
  • And those 45 to 54 years old are most likely to factor in their mortgages (40 percent). That's compared to 21 percent of those 18 to 34 years old and 24 percent of those 55 years and older who factor in mortgages.

The survey was conducted online by Harris Interactive on behalf of Northwestern Mutual from Aug. 10-14, and included 2,097 American adults ages 18 and older.