Over the years, there has been much debate about counting the day of Pentecost.  Some have said that the Greek word Pentecost means "count 50."  This is not true.  Pentecost merely means 50th and it is the 50th day of the Feast of Weeks.
Before we pursue the counting, we need to thoroughly learn and understand the correct day to begin our count from.  In the modern eras of the Church of God, there has been much confusion on this subject.  The confusion was such that in the largest organization of Holy Day keepers, they actually incorrectly kept Pentecost on a Monday for many years.  When I first came into contact with the Church of God, this was the custom that I was taught.  It was sometime before I ever questioned that teaching.  So you see, I have been guilty of keeping it on the wrong day too.
The Sadducees calculated Pentecost from an annual Holy Day during the Days of Unleavened Bread.  Thus, like other Holy days, it always fell on a different day of the week, but this was wrong.  In this day and age, there are still people that believe in this practice.  It is not the purpose of this article to spend our time going through all of these mistaken teachings.  Rather, I want us to look at the biblically instructed method of counting the 50 days to Pentecost.  Leviticus 23 gives us detailed instruction on keeping all of the annual Holy Days.  It gives specific details in chronological order and is without doubt, the clearest set of instructions God has given us. 
Before I proceed with the explanation, I want us to look at Leviticus 23 and understand why the imistakes of the past were made.  The failure to understand and acknowledge a whole 50 day long Holy Day season is the prime reason for the mistakes in arriving at the proper date for Pentecost. 
After all in the Old Testament, it was not simply called Pentecost, it had a different name clearly stated in Leviticus 23.  The "50th day" was it's name because it was the culminating day of the 50 day long Feast of Weeks.  This Holy Day season is the longest festival in God's Holy Day Calendar.  So you see, that for many years, church organizations and calendar gurus have ignored 49 days of this important festival.  They only acknowledged Pentecost, the 50th day, which is the only Holy convocation during the 50 day long Feast of Weeks.  Note that the Feast of Weeks overlaps the Days of Unleavened Bread, but Leviticus does not assign any Holy Days other than Pentecost to the Feast of Weeks.
Leviticus 23:10-16 says,
10 Speak unto the children of Israel, and say unto them: When ye are come into the land which I give unto you, and shall reap the harvest thereof, then ye shall bring the sheaf of the first-fruits of your harvest unto the priest.
11 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.  
12 And in the day when ye wave the sheaf, ye shall offer a he-lamb without blemish of the first year for a burnt-offering unto the LORD.  
13 And the meal-offering thereof shall be two tenth parts of an ephah of fine flour mingled with oil, an offering made by fire unto the LORD for a sweet savour; and the drink-offering thereof shall be of wine, the fourth part of a hin.
14 And ye shall eat neither bread, nor parched corn, nor fresh ears, until this selfsame day, until ye have brought the offering of your God; it is a statute for ever throughout your generations in all your dwellings.  
15 And ye shall count unto you from the morrow after the day of rest, from the day that ye brought the sheaf of the waving; seven weeks shall there be complete;  
16 even unto the morrow after the seventh week shall ye number fifty days; and ye shall present a new meal-offering unto the LORD.
This gives us  clear details on how to count the 50 day long Feast of Weeks.  In verse 15 it tells us to begin the count from "the morrow after the Sabbath in the Days of Unleavened Bread."  It plainly tells us to count off the 7 Sabbaths or 7 weeks that follow it.  And then the 50th day is Pentecost. 
You cannot follow these instructions correctly if you count from an annual Holy Day.  To meet the criteria of verse 15, you must count off 7 weekly Sabbaths.  That is why it is called the FEAST OF WEEKS, we are instructed to count 7 complete weeks from on Sabbath to another.  Pentecost, the 50th day always falls on the day after the last Sabbath--- thus you have back to back Sabbaths.  You have a weekly Sabbath with a Holy Day back to back.
Leviticus 23:15 say "seven Sabbaths shall be complete."  And the 50th day was the last day of the Feast of Weeks.  It fell right after the seventh Sabbath.  This is counted exactly the same way that the Jubilee Sabbatical years were counted.  Leviticus25:8 says to count off 7 Sabbaths of years (49 years) and the 50 year was the release year or Jubilee.  So you can plainly see that this system of counting Pentecost matches God's system of counting.
It is important that we understand the Biblical names that we use for the Feast of Weeks. The Old Testament also calls it the Feast of First Fruits.  This terminology is very important in helping us to understand the deep prophetic information given in Leviticus 23.  You might say what is prophetic?  Lets' go back to chapter 10.  We see that in the original command, this festival was not to be observed until a future point in time.  Only after the children of Israel had harvested their first harvest in the promised land, were they to keep this festival.  (This it is called the Feast of First Fruits.)
Most people fail to realize the implication of this festival to the New Testament church and that Pentecost is the birth day of the Church of God.  Prior to Jesus Christ death, burial and resurrection, there were no first fruits.  Romans 8:28-30 says, "For those God foreknew he also predestined to be conformed to the likeness of His Son, that He might be the firstborn among many brothers."  So you can plainly see why the term Feast of First Fruits is
so important to the New Testament church.  After Christ's resurrection, and the day of Pentecost, individuals began to be added to the roles of the First Fruits.  When you consider the fact that these festivals were commanded to the children of Israel anciently, it is apparent that they were prophetic and began to be fulfilled on the day of Pentecost and continue to be fulfilled to this very day, as the role book of the First Fruits is still open to those who are called and qualify.
The name Feast of Weeks is used primarily to show us how to count this Holy Day season, and this Holy Day season which lasts for a full 50 days, not just one day.  As God's people we should be mindful of it's deep spiritual meaning and reflect on that meaning during that 50 day period.
Lets look again at Leviticus 23:10 and look in detail at how we establish the day that we begin to count the seven weeks.  God's instruction is, "on the first day of the Feast of Weeks (the Wave Sheaf which is the morrow after the Sabbath during the Days of Unleavened Bread.)  This specific day is mentioned 8 times by name in the New Testament and is called the "First Day of Weeks" because it is in reality the first day of the FEAST OF WEEKS.
The first day of the Feast of Weeks also called "the day of the Wave  Sheaf offering" are very important and have a deep spiritual meaning for the New Testament Christian.  This was the day following Christ's resurrection and the day that His sacrifice was accepted by God.  Thus fulfilling the fact that Jesus Christ was the FIRST OF THE FIRST FRUITS.
A last comment for your consideration, please take a new look at the book of Hebrews and understand that it is truly the epistle to the FIRST FRUITS.  


How an annual Sunday (the first day of the Feast of Weeks)
was mistakenly used to "prove" a weekly Sunday Observance.