Service frm mid-month -what will be due date for paying st?

1. ST liability arises on the date of invoice (i.e. 14th) and the due date for payment is 6th of subsequent month
2. However, since you are an individual, ST is payable on quarterly basis and further you have an option to pay service tax on receipt basis (provided turnover in previous/current year is <=Rs.50 lacs)
3. Assuming that your turnover is within the limit, you are liable to pay ST on receipt basis quarterly. Hence, since you have received payment on 21st nov, you need to pay ST by 6th Jan 2016 for Q3 (oct-dec)

Thanks a lot for the prompt response. 

Yes, my turnover in current year is <=Rs.50 lacs.

Additionaly 

My assumption is, since it is less than 6 months from payment date, I am liable to pay interest at yearly 18%,

Suppose I will pay ST Today that is 8th Feb 2016, and the daue date was 6th Jan 2016. 

So I will pay interest @  18% year for number of days lapsed between 6th Jan 2016 and 8th Feb 2016. 

Please let me know if my assumption is correct. 

No, due date itself for payment of ST is 6th Jan. So interest is payable from 6th Jan till date of payment. Rate of interest is 15% not 18% (because if PY turnover is <=60 lacs, 3% concession is available)

Thanks for the clarification...

While paying service tax online, I can see three fields against accounting code  - Service Tax, Interest Tax and Penalty.

I am about one month late in paying the service tax. Interest becomes say Rs. 500.

My question is, against which field should I pay Rs. 500 Interest Tax or Penalty?