Answer: If you are using the Gregorian calendar with “unbroken chains of weeks” then it will appear to begin on any day of the week. However, Scripture is our standard and it states that the spring Feast of Unleavened Bread commences on the day following Passover the 14th. Counting from the New Moon, it is the 15th day of the month of Abib, and always commences on the seventh-day Sabbath, making the first day of this seven-day feast, a High Sabbath each and every year. This festival ends on the sixth-day of the week, the 21st day of the month, which is also appointed as a holy convocation, but not a seventh-day Sabbath. The day following the 21st is the seventh-day Sabbath each and every year. The Feast days, together with the seventh-day Sabbaths create a GPS for discovering the structure of the Creator’s appointed and true calendar.
And on the fifteenth day of the same month is the Feast of Unleavened Bread to Yahuwah; seven days you must eat unleavened bread. On the first day you shall have a holy convocation; you shall do no customary work on it. But you shall offer an offering made by fire to Yahuwah for seven days. The seventh day shall be a holy convocation; you shall do no customary work on it. Lev 23:6-8