Okay so...
I've taken both the ACT and SAT and both are similar scores infant my SAT is slightly higher. On college vines chancing simulator it tells me I have a 5% more if I use my ACT but I don't understand why.
Yes, this makes total sense because test score thresholds for ACT and SAT tests at colleges vary, there is no standard. It's a mistake to assume that colleges give the same weight to the ACT vs SAT or that they use the CollegeBoard or ACT.org table they do not. The admit results in the CDS' reported suggest that there is some bias.
First make sure you are using the latest concordance calculator or table, either one of these should work.
https://www.act.org/content/act/en/products-and-services/the-act/scores/act-sat-concordance.html
https://satsuite.collegeboard.org/media/pdf/guide-2018-act-sat-concordance.pdf
Second, keep in mind that some colleges are either SAT biased or ACT biased and you can determine that by looking up their most recent common data sets. So in the case of say Univ.NotreDame if you look at the 2021-22 CDS their 50% range is 1410 to 1550 for the SAT and 32 - 35 for the ACT. A 1410 would be a 31 ACT, not a 32. so this means that at ND where they get more ACT scores so they are willing to take a lower SAT score. Does that make sense to you?
If you look at Stanfords latest CDS their SAT range is 1470-1560 and their ACT range is 34-35. But a 33 ACT score is a 1470. So at Stanford its better to submit your SAT score than your ACT score if that makes sense.
Remember that each college has their own admissions team and their own policies and thresholds about what test score meets their academic standard. There is no uniform rule that applies to say all the Ivys. Therefore you have to deeply research each school okay?
Good luck.
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