Period of the caliphate of the first four Caliphs
23-9-2004 | IslamWeb
Question:
I would like to know how long did the reign of the four Khulafa' last, i.e. from Abu Bakr, to 'Ali, may Allaah be pleased with them. How many years did they rule the Ummah after the death of our beloved Prophet, sallallaahu alayhi wa sallam. Please provide proofs from the book of Ahadeeth or authentic book of the Seerah.
Answer:
All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and Messenger.
The period of Khilaafah (caliphate) was thirty years as it is reported in some narrations. The Prophet, sallallaahu ‘alayhi wa sallam, said: “The period of caliphate in my nation will be 30 years, then it will be a kingdom.” Safeenah 
who was a slave of the Prophet, sallallaahu ‘alayhi wa sallam, and who narrated the above narration, said, “We counted the caliphate of Abu Bakr, then he said, the caliphate of ‘Umar and ‘Uthmaan, then he said, and the caliphate of ‘Ali, and we found that it was thirty years.” [Ahmad] After these 30 years, Al-Hasan ibn ‘Ali took over from his father ‘Ali for a period of six months and few days, as Jalaalud-Deen As-Suyooti
stated. So the caliphate of Abu Bakr was from 11 A.H. to 13 A.H., the caliphate of ‘Umar was from 13 A.H. to 23 A.H., then the caliphate of ‘Uthmaan was from 23 A.H. to 35 A.H., and from 35 A.H. to 40 A.H. was the caliphate of ‘Ali .
Al-Hasan abdicated from the caliphate in 41 A.H. So the thirty years of caliphate were completed with the caliphate of Al-Hasan after the death of the Prophet, sallallaahu ‘alayhi wa sallam. After this, the era of kingdom started. The authors who were relied upon in this subject are Ath-Thahabi (At-Taareekh Al-Kabeer), Ibn Katheer (Al-Bidaayah Wan-Nihaayah), and As-Suyooti (Taareekh Al-Khulafaa') 
all.
Allaah Knows best.