“The most widely accepted date for Jesus’ crucifixion is 30 A.D. Careful students will observe that biblical historians repeatedly refer to this date. Any calculations designed to establish the date of His death must take into account that Jesus came to Bethany six days before Passover (Jn. 12: 1). Passover, which identifies the day the lamb was killed (Mk. 14:1,12; Lk. 22:1,7), came on the 14th day of the first month, Abib or Nisan (Ex. 12:6; Lev. 23:5). The 14th did not come on the same day of the week each year. In the year Jesus was crucified, the 14th came six days after Jesus came to Bethany. This is significant because, if we count those six days from the first day of the week, Passover would come too late in the week to fit the biblical narrative. If we back up, we must back over the Sabbath to Friday to begin our count, otherwise Jesus and many other Jews violated at least the traditional Sabbath observance by making such a long journey on that day. These guidelines establish that in the year our Lord was crucified Passover fell on Thursday.”
This is from an article titled “The Crucifixion Date” by Arthur M. Ogden that can be found at http://www.truthmagazine.com/archives/volume28/GOT028159.html