The word Easter appears this one time in the entire Bible --and it is a mis-translation:
Acts 12:4 And when he had apprehended him, he put him in prison, and delivered him to four quaternions of soldiers to keep him; intending after Easter to bring him forth to the people.
PASCHA mistranslated "Easter" in Acts 12:4. A.V., denotes the Passover (R.V.. The phrase "after the Passover" signifies after the whole festival was at an end. The term Easter is not of Christian origin. It is another form of ASTARTE, one of the titles of the Chaldean goddess the queen of heaven. The festival of Pasch held by Christians in post-apostolic times was a continuation of the Jewish feast, but was not instituted by Christ, nor was it connected with Lent. From this Pasch the Pagan festival of Easter was quite distinct and was introduced into the apostate Western religion, as part of the attempt to adapt Pagan festivals to Christianity." Expository Dictionary Of New Testament Words W. E. Vine
Passover is calculated from the appearance of the NEW MOON of Nisan. When Christ rose from the dead, he fulfilled this scripture*:
"Speak unto the children of Israel, and say unto them, When ye be come into the land which I give unto you, and shall reap the harvest thereof, then ye shall bring a sheaf of the firstfruits of your harvest unto the priest: And he shall wave the sheaf before the LORD, to be accepted for you: on the MORROW AFTER THE SABBATH the priest shall wave it." Leviticus 23:10-11
The phrase "morrow after the sabbath" always refers to the sabbaths of the Jewish festivals and not the weekly sabbath.
Since some people ask why do you think Easter is celebrated on Sunday? I will tell you why: "Easter was introduced into the apostate Western religion, as part of the attempt to adapt Pagan festivals to Christianity."
* "But now is Christ risen from the dead, and become the firstfruits of them that slept."1 Corinthians 15:20
"For I delivered unto you first of all that which I also received, how that Christ died for our sins according to the scriptures; And that he was buried, and that he rose again the third day according to the scriptures:" 1 Corinthians 15:3-4