The Christian Passover, which renews the New Covenant relationship, should be observed only once a year on the 14th day of the 1st month, the month of Nisan, according to the calculated Hebrew calendar. Since the Bible reckons each day from sunset to sunset, the Christian Passover observance is to be held after sunset of the 13th day of the 1st month, which is actually the night of the 14th day of the 1st month. Remember that today the Jews do not keep a 14th Passover at all. The Jewish “Passover” is observed a day late and is combined with the Feast of Unleavened Bread, which begins on the 15th day of the 1st month and continues for seven days. In violation to the clear Scriptural commands, the Jews have added an eighth day to their “Passover,” extending it to the 22nd of the 1st month. (For a full explanation read The Christian Passover by Fred R. Coulter.)
In order to know when the Passover day falls according to the calculated Hebrew calendar, as synchronized with the Roman calendar, see The Comprehensive Hebrew Calendar by Arthur Spier. This book shows the calculated dates to the year 2100. However, for your convenience, the dates for the annual festivals of God from the years 2003 to 2010 as they occur according to the Roman calendar, is provided on page 29. The New Covenant Passover service is to be observed annually “until the Lord may come.”