athasau yuga-sandhyayam
dasyu-prayesu rajasu
janita visnu-yasaso
namna kalkir jagat-patih
SB 1.3.25

Translation
Thereafter, at the conjunction of two yugas, the Lord of the creation will take His birth as the Kalki incarnation and become the son of Visnu Yasa. At this time the rulers of the earth will have degenerated into plunderers.

Purport by Srila A.C. Bhaktivedanta Swami Prabhupada
Here is another foretelling of the advent of Lord Kalki, the incarnation of Godhead. He is to appear at the conjunction of the two yugas, namely at the end of Kali-yuga and the beginning of Satya-yuga. The cycle of the four yugas, namely Satya, Treta, Dvapara and Kali, rotates like the calendar months. The present Kali-yuga lasts 432,000 years, out of which we have passed only 5,000 years after the Battle of Kuruksetra and the end of the regime of King Pariksit. So there are 427,000 years balance yet to be finished. Therefore at the end of this period, the incarnation of Kalki will take place, as foretold in the Srimad-Bhagavatam. The name of His father, Visnu Yasa, a learned brahmana, and the village Sambhala are also mentioned. As above mentioned, all these foretellings will prove to be factual in chronological order. That is the authority of Srimad-Bhagavatam.