Tsukuba study finds people underestimate their lifespan by 59%

September 4, 2026 at 06:39 PM2 min

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A 28-year study of 2,447 Japanese adults found that people who expected to live longer did live longer, but 59% underestimated their actual lifespan. Researchers from the University of Tsukuba linked the underestimation to anchoring on average life expectancy at birth.

Key Facts

The study tracked 2,447 adults aged 60 and older from 1996 for 28 years, during which 1,514 participants died.
Participants who expected to live longer had statistically longer survival, according to official death records.
59% of participants lived longer than they had predicted, with many anchoring their estimate to the average life expectancy of 80 years.
Researchers warned that underestimating lifespan can lead to inadequate retirement savings and premature depletion of funds.
More educated participants were less likely to choose round numbers like 75, 80, or 85, but they still underestimated their lifespan.

Study Design and Findings

The study, led by social scientist Shohei Okamoto at the University of Tsukuba, began in 1996 and followed 2,447 adults aged 60 and older for 28 years. At the start, participants were asked how long they expected to live. By the end of the study, 1,514 participants had died, and their official death records were compared with their initial predictions. The analysis showed that those who expected to live longer did, in fact, survive longer, a result the researchers said could not be explained by positive thinking alone. The researchers suggested that people have deeper internal knowledge about their own health, hidden habits, and family history.

The 59% Underestimation

Despite the accuracy of some intuitions, 59% of participants lived longer than they had predicted. The researchers attributed this to anchoring on the average life expectancy at birth, which was around 80 years at the time. Many participants chose 80 as their predicted lifespan, but a person who has already survived to age 70 has a much higher remaining life expectancy than a newborn's average. The study also found that more educated participants were less likely to choose round numbers divisible by five, such as 75, 80, or 85. However, even educated participants underestimated their own lifespan and lived beyond their predictions.

Financial Consequences

The research team emphasized that mispredicting lifespan is not merely a philosophical curiosity but can lead to economic hardship. Underestimating life expectancy can cause people to prepare insufficient retirement funds and run out of money early. Conversely, overestimating lifespan can lead to unnecessary frugality and a risk of poverty in old age. The scientists called for more transparent public information about remaining life expectancy based on current age and sex to help people make better financial and life decisions.