little by little vs in stages

little by little and in stages both are adverbs.

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

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

Other synonyms of little by little include bit by bit, piecemeal.

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