How do you actually calculate how much cashback you get from your credit card spend?

I am using miles card but I guess the method behind is the same.

I use excel. I copy every transaction from my statment and then apply formula.

Most of the time, it tally with what the banks give me. If it don't, I will just call them up and most of the time, it is because the MCC is different. Otherwise, they will look into it and then gives you the points (or cashback) after their investigation.

Hope this helps!