This is also relevant:
Biblical New Year? Not in my Bible!
In some heretical Jewish sects, and especially in their online versions, one sees the New Moon of Nisan referred to as Biblical New Year. The supposed basis for this assertion is Exodus 12:2 "This month will be for you the first of months". Indeed, the months of the Jewish calendar are numbered from Nisan (called in the Torah "The Month of Spring"). People are often confused when they find out that Rosh HaShana, the "real" Jewish New Year" is in the seventh month! Yet, we never find the first of Nisan referred to in Scripture as the "new year", nor do we find any special observances for this New Moon more than the others. The sacrifices of the Temple were the same. No special ceremonies were ordained to mark this New Moon more than others. The problem here is that New Year has a totally different meaning in the context of Torah, from our modern concept of celebrating January 1st. The New Year, or, more correctly, the New Years, are the dates marking shifts in status of various things. A modern example is that race horses, when said to be two or three years old, are counted from January 1st. A horse born anytime between January 2nd to December 31st, becomes one year old on January 1st. Similarly,, in the Jewish calendar, we have four such "New Years".The first of Nisan is the New Year for dating the reign of Kings, and for setting the order of festivals. Therefore, Passover, which occurs in Nisan, is considered the first festival of the year. The first of Elul is the New Year for tithing animals. One may not tithe animals of different ages together. Like the race horses, their age is determined by the first of Elul. This, too, has no special ceremonies.The first of Tishri,that we actually call "Rosh HaShana", establishes the years for Sabbaticals and Jubilees, agricultural cycles of grains and vegetables, as well as the divine Judgement made for every person. It is not so much a day of celebration, as of introspection. The Torah calls it "the Day of Remembrance". We find the month of Tishri, the Seventh Month, referred to as the New Year twice in Scripture. One time is in Exodus 34:22, with the Sukkot holiday (which occurs in the Seventh Month) referred to as "the Feast of the Harvest, at the return (renewal) of the year". In Ezekiel 40:1, the prophet speaks of a revelation on "Rosh HaShana, at the tenth of the month". The Tenth of Tishri is Yom Kippur, There is no special observance connected with the tenth of Nisan.The fourth Rosh Hashana is the fifteenth of Shevat, the New Year of the Trees, when the trees are considered one year older, which has implications for tithing of fruit, as well as fixing the first three years of a tree's life, when its fruit is forbidden ('orlah). Sabbatical year laws regarding fruit are also dependent on the fifteenth of Shevat. It should be noted that the years marked on the Jewish calendar today, originate from a Second Century work called "Seder Olam". Before that, years were marked by the reigns of Kings, later replaced in most Mediterranean lands by years marked from the reign of Alexander the Great. This was the dating system in force in Talmudic times, and is still used by the Yemenites. Other Jewish communities employ the system of the Seder Olam. Each of these days is significant. But only the First of Tishri is marked by special observances, and has become known as Rosh HaShana.