What a 1/5 rating means
On the comedogenic scale, a 1 sits at the safe end of the scale — clogging is unlikely for most people. That places Calendula in the range most people, including many with acne-prone skin, tolerate well.
One thing the number cannot tell you is concentration. Ingredients are listed in descending order, so Calendula near the end of a label is present in tiny amounts and matters far less than the same ingredient near the top.
About Calendula
It is a botanical extract included for soothing or marketing appeal. A soothing marigold extract rated 1/5.
On a label it can read as Calendula, Calendula Officinalis Extract — worth knowing when you scan an ingredient deck.
Calendula in makeup and skincare
It appears in 'natural' complexion products and soothing skincare. Its irritancy is rated separately at 0/5, which is low.