Trying to figure out the formula for the interest calculation . Reviewed a prior year statement when I actually had to carry a CC balance (below). Not able to figure out how the average daily balance is calculated to determine 'balance subject to interest rate'. Once I figure this out this formula comes close enough for me to what the interest charge was:
=3513.9*((1+(0.105/365))^30)-3513.9
Not worried about being a bit off but would like to know how to calculate. Anyone want to take a stab at it? FYI - current interest rate is 8.25%
You'll need the calendar and the statement date, but roughly, add your balance on day one to your balance on day two to your balance on day three, etc... up to and including day 30.
Divide sum by 30.
That's your average daily balance. 
Duh 
That comes close enough. Bless you