often vs ofttimes

often and ofttimes both are adverbs.

Word	Noun	Adjective	Verb	Adverb
often	No	No	No	Yes
ofttimes	No	No	No	Yes

As adverbs, often and ofttimes are synonyms defined as:

Other synonyms of often include frequently, oft, oftentimes.

often (adverb)	ofttimes (adverb)
many times at short intervals	many times at short intervals
frequently or in great quantities
in many cases or instances