February 27th, 2021
The 22nd ammendment was passed by Congress March 21, 1947 and ratified on February 27, 1951. It stated:
No person shall be elected to the office of the President more than twice, and no person who has held the office of President, or acted as President, for more than two years of a term to which some other person was elected President shall be elected to the office of President more than once.
Source: constitutioncenter.org/timeline/html/cw10_12240.html