Lord Kalki, an avatara of Vishnu, appears at the final or ultimate moments of the Mahayuga.
Metaphysically, Lord Kalki represents the end of everything: mind and matter, space and time, life and non-life, the cycle of birth and death, all history and memory come to an end with his coming. The universe goes out of existence. But the end of the universe is the fountainhead for the creation of a new universe.
The cycle of a new Mahayuga and new universe begins after the dissolution of the earlier Mahayuga and universe. The Upanishads mention that there are four yugas in every Mahayuga: Krita (Satya), Treta, Dvapara and Kali. The current universe is in Kali Yuga, which began in 3102 BC, and will last for 1200 divine years, or 432,000 human years.
The Puranas describe periods of time much larger than the yugas and the mahayuga—these are called manvantaras and kalpas. One manvantara comprises 71 mahayugas; 14 manvantaras comprise one kalpa, equal to a day in Brahma's life. Thus, a day in Brahma’s life consists of an infinite number of years from the human perspective.
Since Lord Kalki appears at the end of the Mahayuga, it can be surmised that, according to the Upanishads and Puranas, the universe comes to an end and is reborn several times in each manvantara and kalpa. The Puranas talk about thirty kalpas. The present kalpa is the Varaha Kalpa which came after the passage of the previous kalpa, the Padma Kalpa.