According to Hindu Panchang (calendar), a Tithi is a lunar day. As in Vedic timekeeping, there are thirty tithis in each lunar month. The Tithi is counted starting from the new moon day and full moon day like Pratipad, Dwitiya, Tritiya etc. and each is repeated twice in a month. Only New Moon day (Amavasya) and Full Moon Day (Purnima) comes once in a month. Tithis begin at varying times of the day and vary in duration from approximately nineteen to twenty-six hours. The Tithis are as follows -
Pratipad: The governing deity of this day is Lord Brahma, who is god of all types of auspicious and religious ceremonies.

Dvitiya: The ruler of this day is Vidhata and the day is good for laying of foundations for buildings and the other things of permanent nature.

Tritiya:Vishnu is the lord of this Tithi and the day is good for cutting of one`s hair and nails and shavings.

Chaturthi :The death god Yama is the ruler of fourth lunar day. The day is favorable for destruction of the enemies, removal of hindrances and acts of battle.

Panchami : The Moon himself rules the Tithi, and is believed that administering medicine, purging of poisons and surgery becomes successful.

Shashthi :Kartikeya is the ruler of this Tithi and this is good for enthronements, meeting new friends, festivities and enjoyment.

Saptami : This Tithi is governed by Indra. One may begin a journey by conveyances and deal with other things of movable nature.

Ashtami : Vasus preside over the day which is good for taking up arms, building defense and fortification.

Navami : Serpent rules this Tithi, which is suitable for killing enemies and act of violence and destruction.

Dashami : The Tithi is ruled by Dharma and is auspicious for acts of virtue, religious functions, spiritual practices and other pious activities.

Ekadasi :Ekadasi has special significance in Hinduism and Jainism and is observed for fasting. Rudra is the ruler of this day. Fasting, devotional activities and remembrance of supreme Lord are done in this Tithi.

Dvadasi : Sun rules the Tithi, which is worthy of religious ceremonies, lightening the sacred fire and performance of one`s duties.

Trayodasi : Cupid is the ruler of this day, which is favorable for making friendship, attaining sensual pleasures and festivities.

Chaturdasi : Goddess Kali presides over this day and the tithi is worthy of administering poison and calling up spirits and elementals.

Amavasya and Purnima : The Vasve -Devas rule the New moon day or Amavasya and suitable for the performance of Austerity.