later on vs later

later on is not an adjective while later is an adjective.

Word	Noun	Adjective	Verb	Adverb
later on	No	No	No	Yes
later	No	Yes	No	Yes

As adverbs, later on and later are synonyms defined as:

Other synonyms of later on include after, afterward, afterwards, subsequently.

later on (adjective)	later (adjective)
	at or toward an end or late period or stage of development
	coming at a subsequent time or stage

later on (adverb)	later (adverb)
happening at a time subsequent to a reference time	happening at a time subsequent to a reference time
	at some eventual time in the future
	comparative of the adverb `late'