Hello Aspirant! Since you have 6 subjects in your class 11 and 12, the percentage should be calculated by taking the best of 5 subjects that is leaving either one aside. By taking the best marks out of your 5 subjects your class 12 term 1 result be declared. They can even take the average of all the subjects or just take the best 5 subjects. This is how your percentage will be calculated.
Hope this helps!