so far vs up to now

so far and up to now both are adverbs.

Word	Noun	Adjective	Verb	Adverb
so far	No	No	No	Yes
up to now	No	No	No	Yes

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

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

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

so far (adverb)	up to now (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
used after a superlative	prior to the present time
to the degree or extent that