How do you calculate average balance on bank statements?

How do you calculate average balance on bank statements?

The average monthly balance is calculated by adding the ending monthly balance for the period (usually 12 months) and dividing this by the period. e.g. For a period of 12 mos with an ending balance at the end of each month of $12 you would have 12+12+12+12+12+12+12+12+12+12+12+12=144 and 144/12= $12. Therefore the average balance over the period is then $12. Hopes this helps.
It is the sum of the end of day balance in the account for each day in the quarter, divided by the number of days in the quarter.
http://www.hdfcbank.com/personal/accounts/aqb_pop_up.htm#3
The question did not indicate the period. It is the sum of the end of every day balance in the account divided by the period for which calculations are made. To amplify the sum of daily balances will be divided by number of days, if you need average daily balance, and by months in case you need monthly average etc.