Trying to use IF DATE and auto number together in a formula


I am trying to link a date column with the day of a plants life cycle. If a plant was "born' on June 7th (Date column), then I want the "Day of Life Cycle" to be "Day 1" and June 8th to automatically populate as Day 2 of the plants life cycle, and so on. See attached image. This way, I can enter multiple "Tasks" (itemize each task with a separate line) with the same date and it will automatically tell me the number of days that plant has been alive on the date the activity took place (Or will take place). I believe that "Day of the Life Cycle" will be the column where the formula resides.

Thanks in advance!

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