One of the most important factors in preparing financially for retirement is having an idea how long retirement savings will need to last. However, the vast majority of adults know little about how long people tend to live in retirement, which can dramatically impact how financially prepared they are.

According to a report by the TIAA Institute and George Washington University's Global Financial Literacy Excellence Center, only 35% of Americans know the average lifespan of retirees, a worrisome knowledge gap that can keep them from saving enough money to last as long as they live. Only 12% of adults have strong longevity literacy, meaning they could correctly answer three longevity literacy questions, while 31% have weak longevity literacy, meaning they demonstrate a complete lack of understanding of the retirement planning horizon for 65-year-olds. Those with strong longevity literacy are more likely than those with weak literacy to plan and save for retirement while working and they tend to experience better financial outcomes in retirement, the report said.

An equally low share of men and women (only around 10%) show strong longevity literacy. However, significantly more men demonstrate weak longevity literacy compared to women, an interesting finding considering men outscore women in financial literacy. The report theorized that women might score better on longevity because they tend to spearhead health care decisions for their families and serve as caregivers for elderly parents.