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The idea that your personality becomes fixed in adulthood is deeply ingrained. You might think of yourself as an introvert, a worrier, or an organized planner and that’s just who you are.

But it’s not really like that, a massive new study shows.

Researchers report that the Big Five personality traits (extraversion, agreeableness, conscientiousness, neuroticism, and openness) change across adulthood about as much as many aspects of life people already expect to evolve, including health, income, self-esteem, and life satisfaction. Drawing on data from nearly 167,000 people followed over decades, the findings challenge one of psychology’s most persistent assumptions: that personality is fixed.

Testing a Stubborn Belief

The researchers first surveyed 887 adults in the United States, asking how much they believed 25 characteristics change between ages 15 and 90. The list included the Big Five personality traits alongside physical health, anxiety symptoms, income, sleep, exercise, self-esteem, life satisfaction, and social activity.

Most people viewed personality as very stable. They expected money, health, and daily habits to change, but assumed the core self would remain largely intact.

Then the researchers turned to real-world data. The team compared those beliefs with evidence from eight major longitudinal studies spanning the United States, Germany, Australia, and the Netherlands. Together, the datasets followed 166,971 people over many years, allowing researchers to compare changes in personality with more than 20 other aspects of life.

The contrast was striking.

Illustration: ZME Science. The Dynamic Self

Across the lifespan, the Big Five traits continued to shift.

Extraversion and openness generally declined with age, suggesting people became somewhat less outgoing and less interested in novelty. Neuroticism also declined, meaning people tended to become less emotionally reactive over time.

Agreeableness and conscientiousness, meanwhile, generally increased, with people becoming more cooperative, responsible, organized, and dependable.

Some of these trends make intuitive sense. As people age, they often take on careers, families, caregiving responsibilities, and routines that reward patience, reliability, and emotional stability. What surprised the researchers was the scale of the changes.

Extraversion and openness ranked among the top 10 variables with the largest overall declines across the lifespan. Conscientiousness ranked high for total change, making it one of the more dynamic qualities the researchers measured. In some comparisons, it changed more than self-esteem, loneliness, or life satisfaction—variables people often treat as easier to alter.

Meta-analytic change trajectories of standardized variables over the lifespan (ages 15 to 90). Credit: Communications Psychology

To capture these patterns, the researchers measured change in two ways. “Net change” compared personality at two points in life, such as ages 15 and 90. “Cumulative change” measured all movement along the way, including temporary increases and decreases that might eventually cancel each other out. Someone can end up with a similar score decades later while still changing considerably over the years.

Heavily Underestimated

People’s intuitions weren’t entirely wrong. Their estimates for changes in health, income, and other life circumstances often aligned reasonably well with the data.

Personality was the clear exception.

Participants underestimated change in all five Big Five traits. They underestimated personality change in 90% of comparisons for net change and in every comparison for cumulative change.

One reason may be how we think about identity. When people become less anxious, more disciplined, or more patient, they often describe it as finally becoming their “true self” rather than becoming someone different.

Culture helps preserve that idea. Phrases like “stay true to yourself” suggest that each person carries a fixed inner essence. Popular personality tests can strengthen the same impression by sorting people into types.

The study argues for a softer view. Traits are patterns, not life sentences.

The findings do not mean anyone can transform overnight. The study followed averages across large groups, not every individual path. Some people change a lot. Others change little. Life events, relationships, illness, work, and deliberate effort may all shape the route.

Still, the results offer a useful correction. Personality is not separate from life. It develops with it. The person you are now may feel familiar. But over decades, the evidence suggests, you can become strangers.

The study was published in the journal Communications Psychology.