I was scrutinizing my statements recently, and a useful thing I found was that you can get a lot more detail by creating a flex query. You can set it to show things like the exact balance used for each interest rate tier and the collateral posted for short positions. On most days I could exactly calculate the accrued interest, but sometime there was a discrepancy that the flex query resolved.
In my case, sometimes they would slightly tweak the interest rate for a prior day or make some other adjustment, and the difference would be posted to the current day's statement. Also, interest on short sale proceeds seems to only be applied sporadically and then several days' worth gets posted all at once.
In my case, sometimes they would slightly tweak the interest rate for a prior day or make some other adjustment, and the difference would be posted to the current day's statement. Also, interest on short sale proceeds seems to only be applied sporadically and then several days' worth gets posted all at once.