The fiscal system in Iran was supposed to use a solar calendar in order to control set up its functions. This calendar, known in Islamic era as “Sāl i Kharāji” or tax calendar, was used alongside with official lunar calendar and nonofficial solar calendars. The outset of this fiscal year is known as Norouz, but it seems that in spite of similarity, fiscal Norouz has been different from the Norouz of the common solar calendar in medieval Iran. This research is about to recognize Norouz as the outset of the fiscal year. Study of calendar facts and historical texts show that “Tax Norouz” must have been at the summer solstice in 1-4 centuries A.H., thus has been suitable for production and earn procedures and there have been efforts to consolidate it at the date. Also, climate diversity in Iran caused local Norouzes to appear in provinces.