The first day in the first half of Brahmā’s life is called Brāhma-kalpa, which is known as Brāhma-kalpa because Brahmā was born on that day. As described in the Prabhāsa-khaṇḍa, there are thirty days starting with the waxing pratipat-tithi and ending with the dark moon tithi, with names starting with Śveta-varāha-kalpa and ending with Pitṛ-kalpa. This makes one month of Brahmā. These months are repeated twelve times to make one year. Fifty of those years is called a parardha. The first day in the first parardha is called Brahma-kalpa or Śveta-vārāha-kalpa. It is called Brāhma-kalpa because it is Brahmā’s birth tithi. It is described in the astronomical scriptures as occurring on the śukla-pratipat of Caitra month.