Here is my answer:
From Lev 23:9–15, we learn that we’re to begin the count of the omer toward Shavuot (Pentecost) from the morrow/day after the Sabbath when the barley first fruits were presented to YHVH as a wave offering (called wave sheaf day). The question is whether we start the omer count from the Sabbath, or from the day after the Sabbath? Does the Sabbath or the day after the Sabbath (Sunday) have to fall within the week of the Feast of Unleavened Bread? Normally, this isn’t an issue since both the Sabbath and the first day of the week fall within the week of Unleavened Bread. However, this year (2015), this is the case. If you choose to count from Sunday, then the Saturday, April 4 falls outside of Unleavened Bread, but Sunday, April 5 falls within the Feast of Unleavened Bread, since this is the first day of the feast. If you choose to count from the Sabbath that falls within the Feast of Unleavened Bread (i.e., April 11), then this places wave sheaf day outside of the Feast of Unleavened Bread. Those who begin the omer count toward Shavuot from April 5 will be celebrating Shavuot on Sunday, May 24, while those who begin the count from April 12 will be celebrating Shavuot on Sunday, May 31.
So this brings us back to our basic question of when to start the omer count. Does the Sabbath or the day after the Sabbath (Sunday or wave sheaf day) have to be within the week of the Feast of Unleavened Bread? Some people will say say the Sabbath has to be, and some will say the day after the Sabbath has to be. When reading Lev 23:9–15, you really can’t tell which it is. It seems like it could go either way. It’s a tie.
Enter Josh 5:10–11, which is the tie breaker. Those who believe that you start the omer count from the day after the weekly Sabbath use this passage as their proof. Here is my commentary on this passage:
Joshua 5:11, And they ate. As the manna ceased, the Israelites ate the fresh barley grain that had already been growing in the land. In Leviticus 23:14, the Israelites were forbidden to eat of the new barley crop of the land of Israel until the day of the omer offering (or wave sheaf day). This year, the omer offering occurred on the next day after the Passover (Nisan/Abib 14), which was Nisan/Abib 15, or the first day of the Feast of Unleavnened Bread. Because the omer offering was to be brought on the morrow or day after the (weekly, see notes at Lev 23:16) Sabbath (Lev 23:11), this means that the Israelite’s first Passover in the land of Israel occurred on a weekly Sabbath, and wave sheaf day occurred on Sunday. This verse also shows us that the morrow after the Sabbath (i.e., wave sheaf day) occurred during the Feast of Unleavened Bread — not before or after it. This should be taken into consideration when determining which weekly Sabbath at the time of Feast of Unleavened Bread should be used to determine wave sheaf day and, hence, the beginning the omer count. This passage indicates the wave sheaf day, not the weekly Sabbath, has to fall within the Feast of Unleavened Bread.
This passage is circumstantial evidence that the ancient Israelites calculated the omer count based on wave sheaf day, not the weekly Sabbath, having to fall within the Feast of Unleavened Bread. This is why our ministry begins the count of the omer toward Shavuot from the day after the weekly Sabbath, and not the Sabbath itself, that falls within the Feast of Unleavened Bread.
As a footnote, by calculating the omer in this manner, this keeps wave sheaf day (the day Yeshua ascended to heaven and was accepted by the Father) within the Feast of Unleavened Bread, which fulfills biblical types and shadows more accurately than if wave sheaf day fell outside of the Feast of Unleavened Bread. For more info on this, please read my detailed article on the subject at http://www.hoshanarabbah.org/pdfs/firstfruits.pdf
I hope this answers your question.