Neuroscientists Create a Scientific Way to Measure How Multilingual You Really Are

More than half of the global population speaks more than one language, yet science has long struggled with a surprisingly basic problem: there is no clear, consistent way to define what it actually means to be bilingual or multilingual. Some people grow up speaking two languages from birth, others learn additional languages later in life, and many fall somewhere in between. Despite this diversity, research has often relied on vague labels or overly complex questionnaires that fail to capture real-world language ability.

Now, neuroscientists at New York University (NYU) have taken a major step toward solving this issue. A research team has developed a mathematical formula and an accompanying calculator that can quantify multilingualism in a precise, evidence-based way. Instead of simply asking people to identify as bilingual or multilingual, this tool measures how multilingual someone truly is and determines which language is dominant.

The study behind this work was published in the peer-reviewed journal Bilingualism: Language and Cognition, and it offers a new standard for understanding language proficiency across multiple languages.

Why Defining Multilingualism Has Been So Difficult

Language ability is not a single skill. It includes listening, speaking, reading, and writing, and proficiency in each area can vary dramatically from one language to another. Someone may speak a language fluently but struggle to read it, or understand it well without being able to write confidently.

On top of that, people acquire languages at different points in life. A language learned in early childhood often feels effortless, while one learned later may require more conscious effort. Traditional research methods have either ignored these nuances or relied on lengthy background surveys that are difficult to standardize across studies.

As a result, comparing findings across multilingual research has been challenging. Two studies might both include “bilingual” participants while actually examining very different language profiles. This lack of consistency has slowed progress in fields ranging from neuroscience to education and clinical assessment.

A Calculator That Quantifies Multilingualism

To address this gap, NYU researchers Esti Blanco-Elorrieta, an assistant professor of psychology and neural science, and Xuanyi Jessica Chen, a doctoral student, developed a calculator built on carefully designed formulas.

Rather than categorizing people into broad labels, the calculator produces a multilingualism score. This score places individuals on a continuous spectrum ranging from monolingual to perfect polyglot, reflecting both how many languages they know and how well they know them.

In addition, the tool provides a language dominance score, showing which language is strongest by calculating differences in ability across languages.

The Two Core Variables Behind the Formula

The calculator relies on two main inputs, collected separately for listening, speaking, reading, and writing in each language:

1. Age of language acquisition
   Users indicate when they began learning each language for each skill area. This matters because decades of research show that earlier language exposure strongly predicts higher eventual proficiency.
2. Self-rated language proficiency
   Users rate their own abilities across the four language domains. While self-ratings may sound subjective, previous research has consistently shown that they are a reliable and efficient proxy for actual language ability when used carefully.

To address concerns about bias, the researchers incorporated statistical controls designed to minimize the effects of over- or underestimation. This allows the calculator to remain both practical and scientifically sound.

How the Calculator Interprets the Results

Once the data is entered, the formulas generate two distinct outcomes:

• A multilingualism score that reflects the overall degree of multilingual ability.
• A language dominance profile that identifies which language is strongest relative to the others.

Importantly, these results recognize that multilingualism is not an all-or-nothing trait. Someone who speaks three languages at intermediate levels may score differently from someone who speaks two languages with native-like fluency, even though both might casually describe themselves as multilingual.

Broad Language Coverage and Accessibility

One of the strengths of the tool is its inclusivity. The calculator works in nearly 50 languages, including American Sign Language, and it also allows users to manually enter languages that are not already listed.

This flexibility makes it suitable for diverse populations and reflects the reality that multilingualism exists far beyond commonly studied language pairs.

Scientific Validation Across Populations

To ensure the calculator was not just theoretically sound but also practically accurate, the researchers tested it in two distinct groups:

• Healthy young bilingual adults
• Older bilingual adults with language impairments

They then compared the calculator’s results with those produced by traditional, much more detailed language assessment methods. Across both populations, the new formulas produced nearly identical language dominance outcomes to the established approaches.

This demonstrated that the calculator could deliver accurate results with far less complexity, making it easier to use in both research and applied settings.

Why Age of Acquisition and Self-Rating Matter

The inclusion of age of acquisition is especially important. Research in linguistics and neuroscience consistently shows that languages learned earlier in life are more likely to reach native-like proficiency, particularly in pronunciation and grammatical intuition.

Meanwhile, self-rated proficiency has proven to be a surprisingly strong predictor of actual performance, especially when assessed across multiple language domains rather than as a single global judgment. By combining these two variables, the calculator captures both experience and ability in a structured way.

Potential Applications in Research, Education, and Healthcare

The implications of this work extend well beyond academic curiosity.

In research, the calculator offers a standardized, transparent way to describe language backgrounds, improving comparability across studies and strengthening conclusions about how multilingualism affects cognition and the brain.

In education, it could help educators better understand students’ language strengths and challenges, particularly in multilingual classrooms where simple labels often fail to capture real abilities.

In clinical settings, the tool could support more accurate language assessments for bilingual and multilingual individuals, including older adults and those with language-related impairments. This is especially valuable in diagnostics, where misunderstanding a person’s language dominance can lead to inaccurate conclusions.

Understanding Multilingualism as a Spectrum

One of the most important contributions of this work is the idea that multilingualism should be understood as a continuum, not a category. Language ability varies across skills, ages, and contexts, and this calculator reflects that complexity without becoming impractical.

Rather than asking whether someone is bilingual, the tool asks how multilingual they are and in what ways. This shift has the potential to reshape how language ability is discussed in both science and everyday life.

Final Thoughts

Multilingualism is one of the most common human experiences, yet it has long lacked a clear scientific definition. By creating a calculator grounded in neuroscience and linguistics, the NYU research team has provided a practical solution to a longstanding problem.

The result is a tool that is simple, inclusive, and scientifically rigorous, offering clarity where there was once ambiguity. As multilingual populations continue to grow worldwide, approaches like this will be essential for understanding how language shapes the human mind.

Research Paper:
Chen, X. J., & Blanco-Elorrieta, E. (2025). A theoretically driven and empirically grounded calculation for language dominance and degree of multilingualism. Bilingualism: Language and Cognition.
https://doi.org/10.1017/S1366728925100849