Responsa for Rosh Hashanah 3:1
מתני׳ <big><strong>ארבעה</strong></big> ראשי שנים הם באחד בניסן ר"ה למלכים ולרגלים
<big><b>MISHNAH: </b></big>THERE ARE FOUR NEW YEARS.<span class="x" onmousemove="('comment',' I.e.,the year is reckoned to commence at different dates for different purposes, as the Mishnah goes on to specify.');"><sup>1</sup></span> ON THE FIRST OF NISAN<span class="x" onmousemove="('comment',' The first month of the Jewish calendar (in Biblical times known as 'the month of Abib', or the springing corn) , commencing in the latter half of March or the earlier part of April.');"><sup>2</sup></span> IS NEW YEAR FOR KINGS<span class="x" onmousemove="('comment',' If a document is dated with a certain year in a king's reign, the year is reckoned to have commenced in Nisan, no matter in what month the king came to the throne. The Gemara discusses what kinds of kings are meant - whether Israelitish or other.');"><sup>3</sup></span>