Wrong interest calculation from trace.cpc for tds

i have filed a tds return and details are as under

date of payment & deduction is same-25-7-12................4500/-

due date of deposite -07-08-2012

and actual tds deposite is 20-08-2012.

then interest is paid for 1 mnt. or 2 mnt. --------------------1.5% on 4500 is 68

they have calculate on 2 mnth.. is 68*2=135

as far i know interest should be calculate on on month b.coz we have paid on aug.

please reply..................wheter it is true or wrong...........