Why is the date of Zoroaster uncertain?

The date of the prophet Zarathustra—known to the Greeks as Zoroaster—remains uncertain due to the nature of the available historical sources.12

Scholars generally place his life somewhere between 1500 and 600 BCE, with some estimates suggesting the 7th to 6th century BCE and others proposing dates as early as 1500–1200 BCE. This uncertainty arises from several factors:123

• Lack of Contemporary Records: The Gāthās, which are the oldest texts attributed to Zarathustra, do not mention any people or places known from other historical sources, making it impossible to place them in a specific historical context.4
• Oral Tradition: Religious literature in ancient Iran was transmitted orally for centuries. The Avesta, the primary source of knowledge regarding his teachings, was not recorded in writing until long after the language had ceased to be in common use.12
• Method of Transmission: Because the texts were edited and redacted over a considerable span of time, it is difficult to distinguish the original composition from later additions.1

Consequently, while he is traditionally regarded as the founder of Zoroastrianism, there is no secure, fixed evidence to date his life precisely.15