今(temporal counter) vs. 本(temporal counter)

Question

Aside from levels of formality, is there a difference in the meaning/nuance of

今日・今週・今月・今年

as opposed to

本日・本週・本月・本年

?

Answer 1

• 本週 does not exist in the first place. BCCWJ returned virtually zero result, and there is no dictionary entry for 本週.
• 本月 is very rare. Most examples in BCCWJ are either from legal documents or quotes of old documents. I would say you should avoid using this term altogether unless you are a lawyer.
• 本年 and 本日 are relatively common and sound fairly formal and stiff. They are almost exclusively found in formal greetings, announcements and such. 今年/今日 are roughly 10 times more common than 本年/本日, according to the corpus. Grammatically speaking, I think there is no difference in usage; both are used either as nouns or as standalone adverbs. See also: What's the difference between 今日{きょう} and 本日{ほんじつ}?

Answer 2

I don't think there are differences in the meaning at all. The latter sounds just a bit 堅苦しい(stiff/formal).