How long do you think you’ll live?
Most of us can probably come up with a number. Maybe it’s based on how long our parents or grandparents lived, how healthy we feel today, or simply the age we tend to associate with a long life. But how much information does that guess actually contain?
Surprisingly, perhaps quite a bit.
A 2026 study followed older adults in Japan for up to 28 years and found that people who expected to live longer generally did. Their predictions were far from perfect, however, and they shared one particularly interesting bias: people were more likely to underestimate how long they had left than overestimate it.
The researchers, led by social scientist Shohei Okamoto of the University of Tsukuba, used data from the Japanese Aging and Health Dynamics Study, a nationally representative survey of adults aged 60 and older.
In 1996, 2,447 participants were asked what age they expected to reach. While 393 said they didn’t know, the remaining 2,054 gave an answer ranging from 63 all the way to 120.
Researchers then had something unusual: decades to find out how those predictions compared with reality.
Over the following 28 years, 1,514 of the participants who had given an estimate died. Approximately 98% of the recorded death dates came from official resident records or reports from family members.
The comparison revealed that people’s guesses weren’t meaningless. Those who predicted that they would live longer tended to survive longer, an association that remained even after the researchers accounted for factors including age, sex, socioeconomic characteristics, and health.
But people weren’t necessarily good at predicting the exact age at which they would die. Among participants whose eventual outcome could be determined, approximately 59% lived beyond the age they had predicted for themselves.
That said, the relationship was modest in statistical terms. In the researchers’ model, each additional year someone expected to live was associated with only about 0.12 additional years of estimated survival. The predictions carried real information, but they were not precise forecasts.
Why the Number 80 Kept Appearing
The study was conducted in Japan in 1996, when life expectancy in Japan was approximately 80.22 years. Many participants simply chose 80 as their expected age, a number that closely tracked Japan’s widely known national average.
But life expectancy at birth is not the same as the remaining life expectancy of someone who has already reached older age. A person who has survived to 70 has already passed many of the earlier-life risks that contribute to life expectancy at birth. An estimate based on someone’s current age and sex may therefore be more useful than a single figure for the whole population.
The researchers suggest that participants may have anchored their estimates to the familiar national figure of around 80. However, the study cannot establish that this was actually the reason people underestimated their lifespans.
The difference between men and women also illustrates the problem with relying on a combined population average. In 1996, female life expectancy in Japan was 83.59 years and male life expectancy was 77.01 years, a substantial gap that a single national figure could obscure.
The Groups Who Got It Most Wrong
Not all participants were equally inaccurate in their life expectancy predictions. Women and people with more years of education were particularly likely to outlive their expectations, while those in poorer health were less likely to do so.
The education finding came with an unexpected twist. Participants with more schooling tended to avoid round-number answers. They were less likely to choose ages divisible by five, such as 75, 80, or 85. Yet avoiding those round numbers didn’t make their predictions more accurate. They still tended to underestimate their lifespans.
These differences are another reason the researchers argue that more personalized information could be useful. A broad population average doesn’t account for factors such as sex and current age that can substantially change how many years someone might reasonably expect to have remaining.
What This Study Can and Cannot Tell Us
The research, published as a preprint on medRxiv and not yet peer-reviewed at the time of reporting, is observational. It does not show that expecting a longer life extends a person’s lifespan or that positive thinking keeps people alive.
One possibility is that people carry information about their own health, habits, family history, and circumstances that influences both their predictions and their actual survival. Someone who feels healthy, for example, might expect to live longer and also genuinely have a better chance of doing so.
Although the researchers accounted for a range of health and socioeconomic factors, they could not account for everything that might influence both expected and actual lifespan. The study therefore cannot determine exactly why people’s predictions contained useful information.
There are other limitations too. Participants gave their estimates just once, in 1996, with no opportunity to update those predictions as decades passed. A major diagnosis, a medical breakthrough, or the death of a close family member might all shift how long someone expects to live, but the study couldn’t capture any of that.
The data also lacked detailed information on parental longevity. And because the research included only adults aged 60 and older in Japan, its findings may not transfer directly to younger people or to populations with different demographic and health profiles.
The Financial Stakes of Getting Your Lifespan Wrong
Underestimating your own life expectancy isn’t just an interesting psychological quirk. It could affect decisions that have consequences decades into the future.
The researchers point specifically to retirement planning. If someone expects to live for fewer years than they actually do, they may not save enough to support themselves throughout retirement. On the other hand, substantially overestimating lifespan could encourage unnecessary financial restriction.
As the researchers explain, “Underestimating life expectancy may lead to insufficient retirement funds, while overestimating it could result in unnecessary frugality or even poverty.”
Providing people with better information about remaining life expectancy based on their current age and sex, rather than relying on life expectancy at birth, could help them make more realistic financial decisions.
What This Means for You
The practical takeaway from this research isn’t that you should simply try to think more optimistically about your future. It’s that the number you have in your head may contain useful information, but it shouldn’t be treated as a prediction.
It is also worth considering where that number came from. If you’re 65 or 70, the national life expectancy at birth isn’t necessarily the most relevant benchmark. Remaining life expectancy based on your current age and sex can provide a more appropriate starting point.
The Japanese study suggests that our instincts about our own longevity aren’t meaningless. People who expected to live longer generally did live longer. But the most common error went in an encouraging direction: many people had more time ahead of them than they thought.
Disclaimer: This information is not intended to be a substitute for professional medical advice, diagnosis, or treatment and is for information only. Always seek the advice of your physician or another qualified health provider with any questions about your medical condition and/or current medication. Do not disregard professional medical advice or delay seeking advice or treatment because of something you have read here.
AI Disclaimer: This article was created with the assistance of AI tools and reviewed by a human editor.
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