How and when should I chant the Mahāmṛtyuñjaya mantra?

chant it calmly in the morning or evening, commonly 11 or 108 times, as a prayer for strength, healing and peace.

“Oṁ Tryambakaṁ yajāmahe sugandhiṁ puṣṭi-vardhanam, urvārukam iva bandhanān mṛtyor mukṣīya māmṛtāt.” — We worship the three-eyed One, fragrant, who nourishes all; as a ripe cucumber is freed from its vine, may he free us from death, not from immortality. It comes from the Ṛgveda and is also found in the Yajurveda.

Families turn to it in illness, before surgery, during travel, or simply as a daily prayer. Sit facing east or north, light a lamp before Śiva if you can, and chant slowly with a rudrākṣa mālā — 11, 21 or 108 times. When someone is unwell, relatives often share a count of 1.25 lakh between them, or a priest does a formal japa.

It is a prayer for courage and grace, and works best alongside, never instead of, proper medical care.

Source: Ṛgveda (Maṇḍala 7); Yajurveda · Also called the Tryambaka mantra

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