The Hindu calendar is a lunar system, the months corresponding to the phases of the moon and there are twelve months of 29.5 days. Making it a total of 354 days. To rectify the shortfall of days, an extra leap month is added about once every three years. The Hindu calendar is therefore luni-solar, with a precise month and an approximate year.
The Hindu year, starting with Makara Sankranti, is split into two halves and six seasons. There are various ways of reckoning the New Year; most common is the day after the new moon in the month of Chaitra or, in Gujarat, the day after the Diwali new moon. Various eras are used for numbering the years; the most common are the Vikrami Era, beginning with the coronation of King Vikram-aditya in 57 BCE and the Shaka Era, counting from 78 CE. In rituals the priest often announces the dates according to KaliYuga, (see Kala: Time). For these three systems, the year 2000 corresponds to 2057, 1922, and 5102 respectively. Not everyone agrees on the last figure.
Knowing which name a month of Hindu calendar has takes a little time. The system is based on the rashi into which the sun moves within a lunar month, i.e. before the new moon ending the month. There are twelve rashi names, according to the months of Hindu calendar. When the sun moves into the Mesha r?shi in a lunar month, then the name of the lunar month is Chaitra. When the sun moves into Vrishabha, then the lunar month is Vaishakh. Thus the phenomena of naming the months of Hindu calendar continue.
The Sanskrit grammatical derivation of the months of Hindu Calendar, Chaitra and others is the (lunar) month which has its central full moon occurring at or near the nakshatra Chitr? is called Chaitra. Similarly, for the nakshatras Vishakha, Jyeshtha, (P?rva) Ash?dh?, Shravan, Bh?drapad, Ashvin? (old name Ashvayuj), Krittik?, Mrigash?rsha, Pushya, Megh? and (P?rva/Uttara) Phalgun? the names Vaish?kh and others are derived. The months of Hindu Calendar are split into two pakshas of 15 days. The waxing paksha is called shuklapaksha, light half, and the waning paksha the krishnapaksha, dark half.
The Hindu Calendar has two systems for naming months. The amanta or mukhya mana system - a month begins with a new moon, mostly followed in the southern states. The purnimanta or gauna mana system - a month begins with a full moon, followed more in the North states.
The extra months of Hindu calendar are the ones when the sun does not at all move into any rashi but simply keeps moving within a rashi in a lunar month, then that lunar month will be named according to the first forthcoming transit. It will also take the epithet of adhik or "extra". For example, if a lunar month moves beyond without a solar transit and the next transit is into Mesha, then this month without transit is to be labeled adhik Chaitra. The next month will be labeled according to its transit as usual and will get the epithet nija ("original") or shuddha ("clean").
Every two or three years an adhik masa occurs. It is known so to give it a religious name, purushottam = Krishna and comes every 32.5 months. Thus 12 Hindu mas (m?sa) is the same as approximate 356 days, while solar year have 365 or 366 (in leap year) which create difference of 9 to 10 days, which is divided every 3rd year. But no extra months of Hindu Calendar falls during Kartik to Maha.
If the sun transits into two rashis within a lunar month, then the months of Hindu calendar will have to be labeled by both transits and will take the epithet kshay or "loss". They are considered to be a "loss" because in this case, there is only one month labeled by both transits. If the sun had moved into only one rashi in a lunar month as usual, there would have been two separate months labeled by the two movements in question. For example, if the sun moves into Mesh and Vrishabh in a lunar month, then it will be called Chaitra-Vaishaakh kshaya. There will be no separate months made Chaitra and Vaishakh. Akshay masa occurs very rarely. Known gaps between occurrences of kshaya masas are 19 and 141 years. The last lost month of Hindu Calendar was in 1983. January 15 through February 12 was Pausha-M?gha kshay. February 13 onwards was (adhik) Ph?lguna.
Among normal months, adhika months, and kshaya months, the earlier are considered "better" for religious purposes. That means, if a festival will fall on the 10th tithi of the ?shvayuja month (this is called Vijayadasham?) and there are two ?shvayuja months caused by the existence of an adhika ?shvayuja, the first adhika month will not see the festival, and the festival will be observed only in the second nija month of Hindu Calendar. However, if the second month is ?shvayuja kshaya then the festival will be observed in the first adhika month itself.
When two months of Hindu calendar are rolled into one in the case of a kshaya m?sa, the festivals of both months will also be rolled into this kshaya m?sa. For example, the festival of Mah?shivar?tri which is to be celebrated on the fourteenth tithi of the M?gha krishna paksha was, in 1983, observed on the related tithi of Pausha-M?gha kshaya krishna paksha, since in that year, Pausha and M?gha were rolled into one, as mentioned above. When two months of Hindu calendar are rolled into one in the case of a kshaya m?sa, the festivals of both months will also be rolled into this kshaya m?sa.
According to Hindu Shashtra and belief all weekdays have distinct significance. The weekdays are named as Somvar (Monday), Mangalvar (Tuesday), Budhvar (Wednesday), Vrihaspativar (Thursday), Shukravar (Friday), Shanivar (Saturday), Ravivar (Sunday). Each weekday is associated with a specific god and ruled by a specific planet. The days also have various color significance and fasting are observed on those days for special purpose. It is believed that different gods fulfill different desires. One is afflicted by the rage of the gods if they do not show proper respect to the god. There are many ancient stories and legends depicting the glory of various gods or planets as well as the advantage of keeping the fasts on specific days. The stories also narrate the adversities one has to face if they ignore any God or Planet specific for a day.
Somavar: Somvar or Monday is believed to be the day of Lord Shiva. Fasting is observed to propitiate him. The fasting has special significance on the month of Sravan. This day is observed to acquire wisdom or prosperity.
Mangalvar : Mangalvar or Tuesday is observed as day of lord Hanuman. The disciples wear red clothes, shower red flowers and keep fast. Different sacred stories are red and listened by the devotees before breaking the fasting. The fasting is kept to appease planet Mars and get royal patronage, happiness or a son.
Budhavar: Budhbar or Wednesday is related to planet Mercury. It is also thought the day of Shiva. Green color is good for this day. The followers observe fasting and takes meal only once in a day. Mercury brings happiness and deepens love between husband and wife.
Vrihaspativar : The Vrihaspativar or Thursday is ruled by planet Jupiter. It is also commonly termed as Guruvar. The Vrihaspati is the teacher of the gods. The day is also observed to pay homage to Lakshmi Devi to increase wealth and prosperity. The devotees observe fast. They wear yellow clothes, shower yellow flowers and serve yellow colored food.
Shukravar: This day is observed to pacify Shukra God or Venus. Devotees observe fast on Friday or Shukravar. The lord is worshipped with white flowers and rice. The adherents wear white dresses, serve white food like kheer and avoid sour foods. The venus increases love between husband and wife.
Shanivar : The Saturday or Shanivar is governed by Saturn god, who had evil power to cause distress on anybody for a long period. The Saturn god is made of black iron. All black things like black sesame seeds, black lentils, black flowers are the ingredients of the Puja. People wear black clothes, eat lentils and sesame, donate iron, black blanket or oil. The puja and fasting is performed to keep away sufferings and misery.
Ravivar: Sunday or Ravivar is the day of Sungod. He is worshipped with red sandalwood and red flowers. Fasting is observed to achieve prosperity as well as to get rid of various skin diseases.