Many Pagans start their new year at Shadowfest (Oct 31). And to be fair "The Manuals" indicate that the ritual year starts at Shadowfest.
But I've always felt that there were Ritual Seasons which fade out of and into each other. There are no hard and fast rules for when each "ritual season" starts. The environment, which is primarily influenced by the weather but which can be affected by other things as well, influences the edges of these seasons.
The "Growth & Harvest Season" typically includes Summerfest and Cornucopia.
The "Introspective Season" typically includes the Autumn Equinnox and Shadowfest
The "Rebirth Season" typically includes the Winter Solstice and Lupercus.
The "Renewal Season" typically includes the Spring Equinox and Lady Day.
The whole cycle of rituals is designed to work together, to create a web of life, inner and outer life. We have been culturalized to a Cartesian Separatist approach to life. We break things down into their component parts. We categorize things, ideas, experiences, responsibilities. I am wife, mother, breadwinner, supervisor, strega, neighborhood activist... But in reality these are all connected. Experiences and influences of one area or idea affect the others, affect the whole. The rituals both Solar and the monthly Full Moon rituals are designed to ensure that we experience this fullness, this integrated cycle, the web of life.
During Cornucopia we are to review what is good and worthwhile and what can be eliminated. During the Autumn Equinox we are to look at what is passing or has past and work the hidden, introspective aspects of our lives, at Winter Solstice we experience the potential for rebirth in the darkness, at Lupercus we attempt to connect to the past and to what is wild and natural in all of us, at Spring Equinox appreciate tender new growth.
The secular new year starts at the calendar change in January. Considering that this month is named for Janus, a god who looks both forward and backward, it seems that the secular new year works perfectly to bridge the fruits of the Introspective Season to those of the Renewal Season during the Season of Rebirth. So take the time The New Year,the secular world gives you and do as Janus encourages us and look back and forward at the same time and weave your own web of life.