I am a private company...how do I know when my transition date should be?

Transitioning to ASC 842 is required for ALL companies with fiscal periods ending on or after December 15, 2021. That is to say you will be required to transition to ASC 842 for your F'22 year-end.

Your transition date will equal the date that your F'22 period commences on. For example: if your fiscal year runs from July through June your adoption/transition date would July 1, 2022.