Leviticus 23:15 And you shall count for yourselves from the day after the Sabbath, from the day that you brought the sheaf of the wave offering: seven Sabbaths shall be completed. 16 Count fifty days to the day after the seventh Sabbath: then you shall offer a new grain offering to the Lord.
One is to count fifty days after the Sabbath of waving the firstfruits at the Feast of Firstfruits. The count is seven Sabbaths, which 7 x 7 which equals 49 + one day. The dates is from 16 Nisan -5 Sivan.
Acts 1:3 to whom He also presented Himself alive after His suffering by many infalliable proofs, being seen by them during forty days and speaking of the things pertaining to the Kingdom of God. 4And being assembled together with them, He commanded them not to depart from Jerusalem, but to wait for the Promise of the Father, which He said, you have heard from Me: 5 for John truly baptized with water, but you shall be baptized with the Holy Spirit not many days from now.
The forty days after His Resurrection, Jesus appeared to many people. On the fortyth day of Counting Omer Jesus ascended into heaven from Bethany.
Acts.1:3 to He also presented Himself alive after His suffering by many infallible proofs, being seen by them during forty days and speaking of the things pertaining to the Kingdom of God.
Luke 24:50 And He led them out as far as Bethany, and He lifted up His hands and blessed them. 51 Now it came to pass, while He blessed them, that He was parted from them and carried up into heaven.
Acts 1:9-12 Now when He had spoken these things, while they watched, He was taken up, and a cloud received Him out of their sight. 10…This same Jesus, who was taken up from you into heaven, will so come in like manner as you saw Him go into heaven.
Ten days later was the day the Holy Spirit came down on those in the Upper Room (Acts 2:1-4) the day of Pentecost.