in stages vs little by little

in stages and little by little both are adverbs.

Word	Noun	Adjective	Verb	Adverb
in stages	No	No	No	Yes
little by little	No	No	No	Yes

As adverbs, in stages and little by little are synonyms defined as:

Other synonyms of in stages include bit by bit, piecemeal.

in stages (adverb)	little by little (adverb)
a little bit at a time	a little bit at a time
	by a short distance