calculate no. of days if every month has 30 days

Hi all
Please find attachment for kind perusal.

I have received interest at regular intervals i.e. after every 6 months...
while calculating the days for interest every month have 30 days.

If Upto date is > Interest date 2 then days must be calculate from Interest date 1
else interest date 2 has to be consider for no. of days calculation..

I require calculation of no. of days in col D on the basis of interest date 1 (col A) & interest date 2 (col B) till upto date (col G)

thanks in advance

Thank so much