On that day, he will have been in the Chair of St. Peter for 25 years, five months, and one day, surpassing Leo XIII’s pontificate (1878-1903). St. Peter and Pius IX had the two longest pontificates.
According to the Pontifical Yearbook, St. Peter was head of the Church, first in Antioch and then during another 25 years in Rome. He was martyred around A.D. 67 (or A.D. 64, according to other sources).
Pius IX led the Church for 31 years, seven months, and two weeks, from June 16, 1846, until his death on Feb. 7, 1878.
On March 14, John Paul II will have been in the papacy for 9,281 days, counting from the date of his election.