up to now vs hitherto

up to now and hitherto both are adverbs.

Word	Noun	Adjective	Verb	Adverb
up to now	No	No	No	Yes
hitherto	No	No	No	Yes

As adverbs, up to now and hitherto are synonyms defined as:

up to now and hitherto: used in negative statement to describe a situation that has existed up to this point or up to the present time

Other synonyms of up to now include as yet, heretofore, so far, thus far, til now, until now, yet.

up to now (adverb)	hitherto (adverb)
used in negative statement to describe a situation that has existed up to this point or up to the present time	used in negative statement to describe a situation that has existed up to this point or up to the present time
prior to the present time