SubGPA Confusion - OT Master's Application

[xxscarlettexx]

Hi All, 

I was hoping for some advice on how to understand calculating subGPA (using the last 10 full credits, or the last 20 half credits) for someone who hasn't completed the traditional 5 course per semester for Fall/Winter sessions. I'm hoping to get an accurate estimate of the ORPAS subGPA calculation, because I'm trying to figure out if I would make the competitive cutoff for applications. 

In my circumstances in particular, I completed 5 courses per Fall 2016 and per Winter 2017 of 3rd year, but then I also completed 3 credits for Summer 2017 (not sure if this counted as 3rd or 4th year), 3 credits for Fall 2017 and 4 credits for Winter 2018 to finish off my degree. 

From my understanding, it seems that full time (i.e., at least 8 ORPAS defined credits, or 8 half courses per Fall and Winter terms combined) terms are treated differently from courses/credits completed during single semesters (where at least 4 half courses must be completed) and supplemental (so part-time etc.) when calculating the subGPA. I'm not clear on how they would group or average the ORPAS-converted course GPAs in the case of my atypical semester schedule. I was wondering if someone could kindly clear up the confusion for me, and explain how I should be calculating my potential subGPA? It would be really appreciated!

Thanks so much in advance!