The "Last Supper" event of John 13 was at least one to five days before Passover, the 14th (See John 12:1, "6 days before Passover").
John 13:1-5:
(1) Now before the Feast of the Passover, when Yeshua knew that his hour was come that he should depart out of this world unto the Father, having loved his own which were in the world, he loved them unto the end.
(2) And supper being ended, the devil having now put into the heart of Judas Iscariot, Simon's son, to betray him;
(3) Yeshua knowing that the Father had given all things into his hands, and that he was come from Elohim, and went to Elohim;
(4) He riseth from supper, and laid aside his garments; and took a towel, and girded himself.
(5) After that he poureth water into a bason, and began to wash the disciples' feet, and to wipe them with the towel wherewith he was girded.
At this point, the "Last Supper" has already taken place, yet John 18 clearly indicates that Passover hasn't yet occurred (five chapters later).
John 18:28: Then led they Yeshua from Caiaphas unto the hall of judgment: and it was early; and they themselves went not into the judgment hall, lest they should be defiled; but that they might eat the Passover.
