Hi. Is there a context where you can use häufig but not oft (and vice versa)? Or are they synonyms?
There is no adjective for "oft" so for describing a noun you have to use "häufig". E.g. "Das ist ein häufiges Problem." = "That's a common/often occuring problem."
Otherwise, they are pretty interchangable. But I think "oft" sounds often better.
I hope I could be of help.