Interest on tds deducted but not paid

Hi,

I have deducted TDS as on 31.03.2016 but yet i have not deposited the tax to the govt authorities. Now if i want to pay tax than how will be calculation of interest?? the amount of tax is 30000 so the i have to calculate int form march-Aug i.e 6months or 5 months?

if for 6m than rate of Int will be 9% & if for 5 months than rate of int will be 7.5% on the amount of tax i.e Rs. 30,000

Kindly guide.