Apart from the 1.5 million, who will be shifted over the next 30 days, the rest of its pre-paid users are already on per second billing.
The company said that out of its total customer base of over 166 million, nearly 157 million are pre-paid.
Bharti Airtel too announced earlier this week that all its pre-paid customers will be put on per second billing.
"We have always been customer-centric in our approach, offering choice and convenience to customers and hence, we have been providing both PMB and PSB plans to users so far. Henceforth, we will now be offering PSB plan, by default, to our entire base of nearly 157 million existing and new pre-paid users," Sashi Shankar, Chief Marketing Officer, Idea Cellular said in a statement.
With call drops on the rise, Telecom Secretary Rakesh Garg had also said plans where customers get some free minutes and billing is minute-based need to be examined.
Idea said it has spent Rs 4,050 crore (excluding spectrum) in 2014-15 and has increased its capex plan for FY16 to Rs 6,000-6,500 crore.
"The company will continue to invest in expanding its robust network of nearly 1,50,000 cell sites covering over 3,60,000 towns and villages with voice and data offerings on 2G and 3G and roll out 4G LTE services in 10 key markets, starting 2016," it said.