Why does the calendar show two Ekādaśīs — Smārta and Vaiṣṇava (ISKCON)?

Vaiṣṇavas reject an Ekādaśī “touched” by Daśamī before sunrise and fast the next day; Smārtas go by the tithi at sunrise.

A tithi does not line up neatly with a solar day. When Ekādaśī begins a little after dawn, the previous day may still carry Daśamī at the early-morning hour. Vaiṣṇava tradition (followed by ISKCON, many Gauḍīya, Śrī and Mādhva homes) considers such an Ekādaśī “mixed” (viddha) if Daśamī is present at aruṇodaya, about 96 minutes before sunrise, and observes the fast on the following day instead.

Smārta practice, followed by most householders, generally keeps Ekādaśī on the day when it prevails at sunrise. Most of the time both fall on the same day; in some months they differ by one.

There is no right or wrong between them. Follow the sampradāya of your family or guru, and use one panchang consistently rather than switching between apps.

Aruṇodaya ≈ 96 minutes (4 ghaṭīs) before sunrise · Source: Hari-bhakti-vilāsa; Nirṇayasindhu

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