Based on VS based off of [duplicate]

I have used “based on” for the entirety of my life until I went to a UK boarding school where 90% of the time I hear my teachers say “based off of” instead.

For example, ”We will give you your final grades based off of your performance over the past 2 years.”

I happen to have an English tutor and I asked him what’s the difference, then he said he hasn’t heard of based followed by “off of” as an alternative to saying “based on”, all his life. He then remarked “based off of” as rubbish and advised me not to use it. Now I am even more confused. Would you guys use “based on” or “based off of”?

Thank you in advance.

Solution 1:

I cannot tell you what the difference is but I can tell you this:

Based off of is less formal but is used more often in convesation

Based on has been in use for centuries yet based off of is more recently popular

Based on is generally favored as gramatically correct but is not seen as straightforward as someting like would of vs would have