The traditional Zoroastrian calendar, based on a fixed year of three hundred and sixty five days without an automatic leap year mechanism, requires periodic intercalation, the insertion of an extra month, kabiseh, to keep its months aligned with the actual solar year and with the agricultural seasons the religious festival calendar was originally designed to track. Zoroastrian communities in Iran continued this practice of periodic intercalation across the centuries following the loss of Sasanian state sponsorship, but by the eighteenth century, evidence emerging through renewed contact between Zoroastrian communities in Iran and the Parsi community in India revealed that the two communities' calendars had drifted out of alignment with each other by roughly a month, apparently because Indian Parsi communities had not kept pace with intercalations that Iranian communities had continued to perform.
The discovery, which became clear through correspondence and visiting priests in the 1740s, produced genuine alarm within the Parsi community, since it meant that major religious observances, including the New Year festival Nowruz and other calendar dependent rituals, were being kept on different actual days by the two communities despite sharing the same religious tradition and, in principle, the same calendar system.
Attempts to resolve the discrepancy by adopting the Iranian calendar produced resistance from segments of the Parsi community attached to the calendar they had long used, and the resulting disagreement hardened into a lasting division rather than a resolved correction.