(1) "based on" (2) "based off", "based off of", "based around", "based out of", etc. The issue of the usage of (1) vs ( 2) is a controversial one. (1) appears to be much more frequently used both in conversation and in writing, whereas the frequency of usage of (2) has been on the increase in recent years, especially in U.S. conversation. Personally I'd agree that "based on" is much safer to use than "based off of"; however please do refer to the following links and make your own decision. 1) http://www.merriam-webster.com/dictionary/off%20of 2) https://public.wsu.edu/~brians/errors/based.html 3) http://chronicle.com/blogs/linguafranca/2013/10/23/based-off-of-what/ 4) http://www.quickanddirtytips.com/education/grammar/based-off-versus-based-on 5) http://www.ballpoint.com/blog/2012/04/letters-from-the-grammarverse-based-off-is-off-base/

They are relatively the same, and mean the same, BUT "based on" is the more correct use of the preposition in the English language, leaving "based off" as a regional vernacular, meaning that although it is not correct, many people say it and every English speaker would understand you perfectly if you chose to say it also. It is similar the the use of ain't. Although it isn't correct to use, many people do, and all speakers would understand you if you made the mistake.