Availability on input credit

Service tax are payable on receipt basis only.

say if you are billing/debit to your client for Rs. 15000 (12000 bill amt & 3000 service tax) but during the month you realised only  2000 out of 3000 from service tax then you have to deposit the amount Rs. 2000/- by 5th of next month .

for more details please refer to the site of service tax india