Navaratri is celebrated five times a year. They are Vasanta Navaratri, Ashadha Navaratri, the Sharad Navaratri, the Paush/Magha Navaratri and the Magha Navaratri. Of these, the Sharad Navaratri of the month of Puratashi and the Vasanta Navaratri of the Vasanta kala are the most important. The other two are observed by shaktas only.
Vasanta Navaratri: Vasanta Navaratri, it’s nine days are dedicated to the nine forms of Shakti (Mother Goddess) in the month of Chaitra (March–April) and is observed during the Shukla Paksha (waxing phase of moon) of Chaitra. The beginning of this Navaratri also marks the start of the new year as per the Hindu mythological lunar calendar (Vikrami Samvat).
Ashad Navaratri : Ashad Navaratri, also referred to as Gupta, Gayatri or Shakambhari Navaratri, is nine days dedicated to the nine forms of Shakti (Mother Goddess) in the month of Ashadha (June–July). It is observed during the Ashadha Shukla Paksha (waxing phase of moon). This is mostly observed by shaktas only
Sharad Navaratri: This is the most important of the Navaratris. It is simply called Maha Navaratri (the Great Navaratri) and is celebrated in the ‘pratipada’ (first day) of the bright fortnight of the lunar month of Ashvin. Also known as Sharad Navaratri, as it is celebrated during Sharad (beginning of winter, September–October).
Pausha Navaratri: Paush Navaratri is observed during the Pausha Shukla Paksha, the waxing phase of moon, in the month of December–January.
Magha Navaratri: The Magha Navaratri is also a kind of Gupta Navaratri. The waxing phase of moon in January–February marks the beginning of Magha Navaratri.