Why is it difficult to determine exactly when Indo-European language branches separated?

Determining the exact timing of when Indo-European language branches separated is difficult because linguists have not found a reliable, precise method to calculate these dates using linguistic evidence alone.12

While computational methods like glottochronology have been proposed to estimate "time depths" based on vocabulary replacement, they are not universally accepted. Critics argue that the rate of linguistic change is not constant across different languages or even within a single language over time, and that compiling a culturally unbiased vocabulary list is inherently difficult.13

Consequently, scholars rely on "dead reckoning," which involves estimating the degree of difference between languages and comparing those estimates to families with known divergence dates. Because written records are often nonexistent or cover only a small fraction of human history, linguistic findings must be correlated with archaeological evidence to improve accuracy. Even with these efforts, no consensus exists, particularly regarding the early separation of the Anatolian languages, which are the oldest attested Indo-European languages.1452