Nitya-karma (eternal/obligatory duty) denotes the class of Vedic rites that a twice-born person is required to perform every single day without fail, as opposed to kāmya-karma (optional rites for specific desires) or naimiṭṭika-karma (occasional rites on special occasions). The core nitya-karmas include: the three daily sandhyāvandanam (twilight prayers combining ācamana, prāṇāyāma, gāyatrī-japa, and arghya), brahma-yajña (daily Vedic recitation), deva-yajña (fire offerings), pitṛ-yajña (libations to ancestors), and related purificatory acts.
In Śrī Vaiṣṇava theology, the attitude toward nitya-karma undergoes a crucial transformation after prapatti. For the ordinary sādhaka, nitya-karma earns dharmic merit (puṇya) which purifies the mind and prepares it for jñāna or bhakti. But for the prapanna — one who has already surrendered completely to Bhagavān — these rites are no longer performed as upāya (means) to attain any end. They become pure kaiṅkarya (service), done solely because Bhagavān wishes it and because failure to perform them would displease Him. This shift of motive — from fruit-seeking to service — is central to the Śrī Vaiṣṇava post-prapatti ethic.
The ācāryas warn that abandoning nitya-karmas after prapatti, on the mistaken grounds that surrender has made all action superfluous, is a serious error. Piḷḷai Lokācārya and Maṇavāḷa Māmunigaḷ both affirm that the prapanna's continued observance of nitya-karma is itself evidence of his genuine surrender — he acts not to gain, but because his very body and life belong to Bhagavān.