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.