Landmark Study Warns: Average Lifespans May Never Reach 100 Again

A major new study published in the Proceedings of the National Academy of Sciences (PNAS) has delivered a sobering message: the remarkable increases in human life expectancy that defined the 20th century appear to have slowed down — and might not ever return to that earlier pace. The research, conducted by José Andrade, Carlo Giovanni Camarda, and Héctor Pifarré i Arolas from the University of Wisconsin–Madison, the Max Planck Institute for Demographic Research, and the Institut national d’études démographiques, suggests that no generation born after 1939 is expected to reach an average lifespan of 100 years.

This conclusion challenges a long-standing assumption that people in wealthy nations would continue to live longer and longer, generation after generation. Instead, according to the study, the gains in longevity that once seemed unstoppable have begun to plateau, and even under optimistic scenarios, those born after the 1930s are unlikely to see century-long life expectancies on average.

A Century of Rapid Gains — Then a Slowdown

The researchers examined life expectancy trends across 23 high-income, low-mortality countries, drawing on detailed records from the Human Mortality Database. Using six separate mortality forecasting models, they analyzed how life expectancy changed over time and how it is likely to evolve for people born between 1900 and 2000.

From 1900 to 1938, life expectancy in these wealthy nations increased at a remarkable rate — about five and a half months per generation. A person born in 1900 could expect to live around 62 years, while by 1938, average life expectancy had climbed to about 80 years. This period saw extraordinary improvements in public health, medical science, and living conditions. It was the era of antibiotics, vaccines, clean water, and safer childbirth — all of which drastically reduced early-life mortality.

But starting with generations born after 1939, the pace of progress slowed sharply. The study found that the rate of increase dropped to between two and a half and three and a half months per generation, depending on which model was used. That means each new generation born after World War II gained only a fraction of the longevity boost that earlier generations enjoyed.

Why Are We Slowing Down?

The study identifies several reasons behind this slowdown. One of the main explanations is that the biggest past improvements came from reducing deaths at very young ages — especially infant and child mortality. Once those early deaths were minimized through modern medicine and improved sanitation, there was less room left to achieve similar leaps in average life expectancy.

In the early 20th century, a huge portion of the population died in infancy or childhood. As vaccines, antibiotics, and public health infrastructure improved, those early deaths fell dramatically, driving a surge in average lifespan. But now, in high-income countries, infant mortality is already extremely low, and preventing deaths in the elderly is a much slower, more complex challenge.

The researchers explain that future gains now depend primarily on extending survival at older ages, and that’s inherently harder. While modern medicine can manage chronic diseases and prolong life, the improvements come in small increments, not in the large leaps that earlier medical revolutions achieved.

Even if survival rates among adults improved twice as fast as current trends suggest, the researchers estimate that average life expectancy would still fall short of the explosive growth seen during the early to mid-20th century.

The Role of Mortality Forecasting

To make these projections, the team used mortality forecasting models — statistical tools that predict future death rates based on historical patterns. By running six different models and comparing their outputs, the researchers ensured their results were not an artifact of any one method.

All six models told a consistent story: a deceleration in longevity gains. Even under the most favorable assumptions, no generation from 1939 through 2000 was forecast to reach an average lifespan of 100 years.

The forecasts indicate that someone born in 1980, for instance, will not live to 100 years old on average. While there will always be individuals who surpass 100 — and even 110 — the study’s focus is on average life expectancy across a generation, not the most extreme cases.

What This Means for the Future

This research doesn’t suggest that humanity has hit an absolute biological ceiling, but it does warn that further gains in longevity will likely be smaller and slower. Governments and individuals may need to adjust expectations around retirement planning, healthcare, and social support systems.

Slower improvements in life expectancy mean that pension systems and healthcare budgets designed for constant gains in lifespan might face unexpected strain. If people live longer but not dramatically so, social systems may need recalibration to remain sustainable.

On a personal level, life expectancy influences how people think about saving, retirement, and long-term health planning. Slower gains could shift how younger generations plan for their futures — from when to retire to how much to save and how to approach late-life healthcare.

The study’s authors stress that these forecasts are not destiny. They are based on current trends and historical data. Future innovations in medicine, biotechnology, or public health — such as breakthroughs in regenerative medicine or age-related disease prevention — could still push life expectancy higher. However, barring those dramatic changes, the era of explosive longevity growth may be behind us.

The Broader Context: What Life Expectancy Really Means

Life expectancy is often misunderstood. It doesn’t mean how long an individual will live; rather, it represents the average expected lifespan for a group born in a given year, assuming current or projected mortality rates.

There are two main ways to measure it:

• Period life expectancy, which looks at death rates in a specific year and assumes they stay the same in the future.
• Cohort life expectancy, which tracks a specific generation through its lifetime, taking into account changing death rates as the group ages.

This study focuses on cohort life expectancy, which gives a more realistic picture of how long people in each generation are likely to live, since it accounts for future improvements in healthcare and living conditions.

Are We Nearing a Biological Limit?

The idea that humans might be approaching a natural limit to lifespan has been debated for decades. Some researchers believe there’s a biological ceiling — perhaps around 120 years — beyond which it’s nearly impossible to extend life without fundamentally altering human biology.

Others argue that medical and technological innovations could continue to push that boundary outward. Anti-aging research, gene therapy, and interventions targeting cellular aging are all areas of intense scientific interest. Yet so far, these breakthroughs have not translated into large, population-wide increases in life expectancy.

What’s certain is that the rapid improvements of the early 20th century were unique. They came from revolutionary public health advances that saved millions of lives at young ages. In today’s world, where those gains have already been realized, future progress will likely depend on treating the diseases of aging, which is a much steeper challenge.

Global Implications and Policy Challenges

The slowdown in life expectancy growth has major implications for wealthy nations where aging populations already pose social and economic challenges.

As birth rates decline and populations age, governments will have to support larger numbers of elderly citizens with proportionally smaller working-age populations. This raises questions about retirement age, healthcare funding, and labor force participation.

If average life expectancy stabilizes rather than rises rapidly, some of the long-term demographic forecasts used in policy planning might need adjustment. Pension systems that assume continual gains in longevity could become unbalanced. Healthcare services, too, may need to adapt to the slower pace of improvement — focusing not only on extending life, but on improving quality of life in older age.

What Could Change the Trajectory?

Despite the cautious outlook, several factors could alter the picture in the coming decades:

• Medical breakthroughs: Advances in genetic therapies, personalized medicine, and regenerative technologies might eventually reverse aging-related decline or dramatically reduce deaths from chronic diseases.
• Lifestyle changes: Shifts in diet, exercise, and mental health awareness could improve health outcomes even without major medical innovation.
• Public health preparedness: Better management of infectious diseases, pollution, and global health risks could prevent large-scale setbacks like the COVID-19 pandemic.
• Socioeconomic equality: Addressing disparities in healthcare access and social conditions could yield more consistent health outcomes across populations, indirectly raising average life expectancy.

Still, these are potential influences — not certainties. The authors of the study caution that while the future can hold surprises, the current evidence points to a sustained slowdown in longevity growth under existing conditions.

A Reality Check on Our Expectations

The 20th century gave us astonishing gains in human lifespan — something no previous era had experienced. But this study reminds us that progress is not infinite. The plateau we’re seeing today is a result of success: we’ve already eliminated many of the early-life threats that once cut lives short. What remains are the tougher, slower battles against aging itself.

So while it may be disappointing to learn that no generation after 1939 is expected to reach an average of 100 years, it’s also a sign of how far we’ve come. Living to 80 or 90 on average would have been unthinkable for most of human history.

The takeaway isn’t despair — it’s realism. The age of miraculous gains may be over, but the opportunity to make the later years of life healthier, happier, and more dignified is still in our hands.

Reference:
“Cohort mortality forecasts indicate signs of deceleration in life expectancy gains” — José Andrade, Carlo Giovanni Camarda, and Héctor Pifarré i Arolas, Proceedings of the National Academy of Sciences (PNAS), August 25, 2025.
https://www.pnas.org/doi/10.1073/pnas.2519179122