T-Mobile US Inc reported a better-than-expected quarterly profit and raised its forecast for customer additions for the year as heavy discounting helped attract subscribers.

Shares of the company, controlled by Deutsche Telekom, were up 3.5 percent at $48.40 in premarket trading on Monday.

The company said it now expected to add 3.7 million to 3.9 million branded postpaid customers on a net basis this year, compared with its previous forecast of 3.4 million to 3.8 million.

The Bellevue, Washington-based company added 969,000 postpaid customers in the third quarter ended Sept. 30, up from 890,000 in the second quarter.

T-Mobile and Sprint Corp, have been grabbing market share by gaining subscribers from bigger rivals AT&T Inc and Verizon Communications Inc.

AT&T, which has proposed to buy Time Warner Inc for $85.4 billion, lost 268,000 wireless phone postpaid customers in its third quarter.

Verizon added postpaid subscribers significantly below analysts' estimate for the third quarter.

T-Mobile said it benefited from the launch of the iPhone 7 in the quarter and an increase in branded prepaid customer migrations to postpaid plans.

However, churn, or the rate at which users switch to other networks, increased to 1.32 percent from 1.27 percent in the prior quarter.

On an adjusted basis, the company earned 27 cents per share, according to Thomson Reuters I/B/E/S calculation, beating the average analyst estimate of 22 cents per share.

T-Mobile's net income rose to $366 million, or 42 cents per share, in the third quarter from $138 million, or 15 cents per share, a year earlier.

Net income in the quarter included after-tax spectrum gains of $122 million.

Total revenue rose 17.8 percent to $9.2 billion.

Up to Friday's close, the stock had risen nearly 20 percent this year.

Reuters (Reporting by Aishwarya Venugopal in Bengaluru; Editing by Sriraj Kalluvila and Saumyadeb Chakrabarty)