annually vs per year

annually and per year both are adverbs.

Word	Noun	Adjective	Verb	Adverb
annually	No	No	No	Yes
per year	No	No	No	Yes

As adverbs, annually and per year are synonyms defined as:

annually and per year: by the year; every year (usually with reference to a sum of money paid or received)

Other synonyms of annually include each year, p.a., per annum.

annually (adverb)	per year (adverb)
without missing a year	by the year; every year (usually with reference to a sum of money paid or received)
by the year; every year (usually with reference to a sum of money paid or received)