Festivals that are currently suggested are:

Ostara - Mithraic Easter - Festival of creation and new life - Spring Equinox
Litha - Midsummer Festival - Summer Solstice
Messis - Festival of Harvest and celebration of the produce of life - Autumn Equinox
Mithrakana - ('Festival of Mithras') - Celebration of religious life and religious community - 29th September
Atarkana - ('Fire Festival') - Celebration of the free human spirit, the fire within - November 5th.
Yalda - Re-birth of the Sun - Winter Solstice and following week
including: Bruma (18th to 24th Dec) when the Sun is at its weakest
and Novussol (25th Dec to 31st Dec) when we celebrate the growing strength of the Sun

A Longer List:

Candelakana - 2nd Feb (Candlemas)
This ancient festival marks the midpoint of winter, halfway between the shortest day and the spring equinox. In pre-Christian times, this day was known as the 'Feast of Lights' and celebrated the increased strength of the life-giving sun as winter gave way to spring.

Mortuorum - (or 'Festus Mortuorum')
- Probably a day or period leading up to Ostara
- Oldest traditions are to mourn recently departed dead at the end of the winter season
- "Feast of the Dead"
- "All Souls Day"
- celebrate the spirits of the departed
- invite them to feast with you
- Persian Fravardigan

Ostara - Spring Equinox - about 21st March
- beginning of spring
- celebration of new life
- Persian Nowruz

Zartinatus - 26 March (Natus Zarti)
- birthday of Zarathustra
- celebrate wisdom and enlightenment

Maiakana - 1st May
- fertility, prosperity, burgeoning new life
- celebration of youth/young adulthood
- Spring 'King & Queen'
- Robinus : a lusty and lawless male figure
- Maia (or Maiana) : a goddess of growth
- Persian Maidyozarem (mid-spring)

Litha - summer solstice or midsummer - around 21st June
- water festival
- celebration of defeat of drought by life-giving rain
- ?celebrate physical strength and prowess
- ?celebrate Anahita as goddess of the waters?
- Persian Tirikana

Messis - Autumn Equinox - around 22nd September
- Harvest Festival
- Thanksgiving
- End of summer
- Persian Paitishahem (bringing in the crops) with some features of Mehregan

Mithrakana - 29th September (Michaelmas)
- Festival of Mithras
- Celebrate Mithras and the Good Powers
- Celebrate the Mithraic movement
- Consider how can support Mithras in the coming year and make a 'Mithrakana resolution'

Cyrus Day - 29th October

Atarkana - November 5th
- Fire Festival
- celebration of the life energy
- celebration of freedom
- story of the blacksmith Kavey, the good prince Freydon and the white wizard Albomagus in overcoming the evil tyrant Azidak

Yalda - Winter solstice - Re-birth of the Sun
including: BRUMA (18th to 24th Dec)
when the Sun is at its weakest
and NOVUSSOL (25th Dec to 31st Dec)
when we celebrate the growing strength of the Sun

- or twelve days: 21st dec to 1st jan
after nightfall on 21st dec - death of Mithras?
followed by three days of fasting until
after nightfall on 24th dec - 'Mithraic Breakfast' (makes sense in English language at least) expectation of rebirth celebration
25th december (after sunrise) - epiphany of Mithras (announcement of his re-birth by magi)?

- Persian Yalda and Zayesh Mehr