Three page Excel chart showing the accurate method of calculating the 50 Days of Pentecost starting on Nisan 15, the first day of the Feast of Unleavened Bread, until Pentecost on Sivan 6. Day number one of the fifty days of Pentecost falls on Nisan 16. The Feast of Weeks ends 50 days later on Sivan 6. In 30 AD Nisan 16 was a Sunday and the day of the Resurrection.