Tds calculation

complete as Act states that TDS to be deducted when amount is paid or payable, whichever is earlier

I agree With Kunal.

Thank you Kunal Sir. If a bill has not been paid at all  then is it necessary to deposit TDS?  

yes,

it is necessary to deposit TDS after deducting TDS whether payment made or not

yes you have to deposit TDS by 7th of next month in the month which bill has been posted in books

As pre Sec-194J, Tds on Professional/ Technical service is deducted, date of payment or date of giving credit to the account. Irrespective of received amount, TDS should be deduct on Total Invoice value. 

so TDS is deducte for total value of invoice amount and deposit it before 7th of next month.