The official weekend holiday in Iran is Friday although some public and private sector offices are also closed on Thursdays. The following is a list of public holidays throughout the year. However, it should be noted that the dates on the lunar calendar can not be converted into Christian dates as they change constantly on the solar calendar: Every Friday, the people in Tehran and other Iranian cities perform their Friday prayers ritual. The one held in Tehran at the Tehran University campus is the largest mass of its kind in the region.

Holidays on the Solar Calendar:

1-4 Farvardin (March 21-24) Nowruz (New Year)
12 Farvardin (April 1) The Islamic Republic Day
13 Farvardin (April 2) Late Nowruz holiday (13 Bedar: Nature Day)
14 Khordad (April 4) Imam Khomeini’s demise
15 Khordad (April 5) Ann. 1963 uprising
22 Bahman (Feb. 11) Islamic Revolution Day
29 Esfand (March 20) Nationalization of Iranian Oil Industry

Days of the Week :
There are, of course, 7 days in an Iranian week; however the week begins on Saturday rather than Sunday and thus ends on Friday.
Friday is always a holiday in Iran, although in some offices there is an extended weekend which covers Thursday too.

Holidays on the Lunar Calendar:

9 Moharram: Tasua
10 Moharram: Ashura (Martyrdom of Imam Hossein, AS)
20 Safar: Arbaeen
28 Safar: Demise of the holy prophet(SAWA) and Martyrdom of Imam Hassan (AS)
17 Rabi-ol-Aval: Birth of the holy prophet (SAWA) & Imam Jafar Sadegh (AS)
13 Rajab: Birth of Imam Ali (AS)
27 Rajab: Ordainment Day
15 Shaban: Birth of Imam Mahdi (AJ)
21 Ramazan: Martyrdom of Imam Ali (AS)
1 Shavval: Eid-Al-Fitr
25 Shavval: Martyrdom of Imam Jafar Sadegh (AS)
11 Zilqada: Birth of Imam Reza (AS)
10 Zihajja: Eid-Al-Adha
18 Zihajja: Eid-Al-Ghadir

Please note that the holidays on the lunar calendar have been listed here in the order they were observed in the year 1990-91, corresponding to the solar year 1369 and the lunar Hejirah year of 1410-11. 

NowRuz, NoRooz, NoRuz:( Iranian New Year)

In harmony with the rebirth of nature, the Iranian New Year Celebration, or NORUZ (NowRuz), always begins on the first day of spring. Nowruz ceremonies are symbolic representations of two ancient concepts - the End and the Rebirth; or Good and Evil. A few weeks before the New Year, Iranians clean and rearrange their homes. They make new clothes, bake pastries and germinate seeds as sign of renewal. The ceremonial cloth is set up in each household. Troubadours, referred to as Haji Firuz, disguise themselves with makeup and wear brightly colored outfits of satin. These Haji Firuz, singing and dancing, parade as a carnival through the streets with tambourines, kettle drums, and trumpets to spread good cheer and the news of the coming new year.

The origins of NoRuz are unknown, but they go back several thousand years predating the Achaemenian Dynasty. The ancient Iranians had a festival called "Farvardgan" which lasted ten days, and took place at the end of the solar year. It appears that this was a festival of sorrow and mourning, signifying the end of life while the festival of NoRuz, at the beginning of spring signified rebirth, and was a time of great joy and celebration.