Swedish Twin Research Finds 45% of Investing Behavior Is Genetic

On a recent episode of the My First Million podcast, host Sam Parr walked listeners through a piece of behavioral finance research that could change how investors think about decision-making. Sam highlighted a 2014 Swedish twin study that concluded roughly 45% of savings and investing behavior may be genetic.

Why the Swedish Data Is Unique

The study gained credibility largely because of Sweden’s unusually detailed financial records. Until 2007, Sweden maintained a wealth tax that required citizens to disclose their financial holdings. That created one of the deepest household-level investing datasets ever assembled, allowing researchers to study actual portfolio behavior rather than relying on surveys or self-reported answers.

Researchers then applied a classic behavioral genetics framework. Fraternal twins share roughly 50% of their DNA, while identical twins share nearly 100%. If identical twins consistently display more similar investing behaviors than fraternal twins, even after accounting for upbringing and environment, researchers attribute part of the difference to genetics.

According to Parr, the researcher analyzed roughly 30,000 sets of twins, making the findings difficult to dismiss on statistical grounds.

The Biases That Appeared Genetic

The study focused on several common investing mistakes that financial advisors spend years trying to help clients avoid.

Among the behaviors measured:

• Excessive trading
• Performance chasing
• Home bias
• The disposition effect, or refusing to sell losing investments

The uncomfortable implication is that roughly 45% of investing mistakes may feel like conscious choices but are, in part, genetic. Roughly 55% of behavioral variation still came from environmental factors, education, habits, and systems. That means investors can still improve outcomes, but some people may naturally struggle more with emotional discipline than others.

Each behavior has clear consequences for long-term returns. Over-trading increases fees and taxes. Performance chasing often leads investors to buy near market tops after assets have already surged. Home bias can leave portfolios dangerously concentrated in domestic assets, while the disposition effect causes investors to sell winners too early and hold losers too long.

Practical Takeaways for Investors

For long-term investors, one lesson might be to think about designing systems that compensate for personal weaknesses.

That could mean:

• Automated investing contributions
• Strict position-size limits
• Scheduled portfolio rebalancing
• Rules-based investing frameworks
• Reducing portfolio turnover