It is calculated by simple interest of 3.5% annual means in 1 month interest = deposit (minimum amount between 10th to 31th) * interesst rate (3.5) / 12 *100 .

for example if u hav 10000 minimum amount in ur a/c in b/w 10 to 31th than interest will be = 10000*3.5/1200 = 29.16 rs in that month.

and interest deposit in a/c according to bank rule either half yearly aur quaterly basis... (in ICICI half yeary).