How to decide on Dakshinayana date

In Hindu panchanga, the year is called Samvastara. Each Samvastara has a name. This year 2022 is Shubakrut naam samvastara. 

There are two ayanas in a Samvastara.  One is Uttarayana and the other is Dakshinayana. These Ayanas are generally of 6 months.

The decision of the start day of this Ayana is made based on the Sun transition. When Sun transits to Makara Rashi, that's Capricorn is called Makar Sankranti, and it's the start day of Uttarayana. This usually falls on the 14th or 15th Of January every Year. And when Sun transits to Karka Raashi that's cancer is called Karka Sankranti and it's the start day of Dakshinayana..

This can be usually found in any Hindu panchanga :

Above is Sri Raghavendra Swamy Mutt Mantralaya Panchanga. You can also get the date from the Sun transits in Kundali.

The above reference is for Sun transitions in Kundali on the 16th and 17th of July 2022. You can decide the Dakshinayana and Utaarayana Parva dates based on the Sun transitions.