When to use advisor versus adviser?

Answer 1

I suggest this:

Adviser - one who is available to give advice.

Advisor - one who actually provides advice.

I apply the 'or/ee' principle; 'or' gives, 'ee' receives in the exchange of something. As in offeror and offeree, wherein the offeror gives an offer, and the offeree receives it.

An advisor is actually giving advice to someone in the present. Whereas, an adviser may be simply capable and willing to give, and may have in the past given, advice. An adviser may not be doing so in the present.

Answer 2

"Advisor" is the preferred spelling in American English, while "adviser" is more common in British English. Both words mean the same thing, so you can choose either based on your audience or personal preference.