TalkTalk is offering all its customers a free upgrade to compensate for the recent cyber attack, in which thousands of people's personal data was leaked online.
Dido Harding, chief executive, said that one-off costs were estimated to be in the region of £30 million to £35 million.
"That's covering the response to the incident, the incremental calls into our call centres, obviously the additional IT and technology costs, and then the fact that over the last three weeks until yesterday our online sales sites have been down, so there will be lost revenue as a result," Harding told the BBC.
The contract upgrade will be welcomed by customers who reacted angrily when they were unable to end their contract with TalkTalk without incurring a termination fee, unless money had been stolen from them.
The type of upgrade available to customers will depend on the package they already had, a spokesman said. For example, customers with a TV package might be offered another channel.
Hackers attacked the TalkTalk website on October 21 and accessed the personal details of almost 160,000 customers. The bank details of 15,600 were stolen.
Police have arrested three teenagers and a 20-year-old boy.
