Monday's biggest movers: T-Mobile US sinks 13.3% and Crown Castle jumps 15.6%

Among US-listed companies worth at least $20 billion, the biggest moves in Monday's session (12 October) came from T-Mobile US, which fell 13.3%, and Crown Castle, which rose 15.6%.

The decliners

T-Mobile US (TMUS) fell 13.3% to $148.58. It was its biggest one-day drop since 9 October, based on the past year of closes. The shares are down 25.2% this year and 34.0% below their 52-week closing high. Coverage since the move includes Yahoo Finance's headline “SpaceX's Starlink could pose 3 big risks to Apple, BofA warns”.

AT&T (T) fell 10.8% to $22.18. It was its biggest one-day drop since 9 October, based on the past year of closes. The shares are down 9.5% this year and 22.7% below their 52-week closing high. Coverage since the move includes Yahoo Finance's headline “SpaceX's Starlink could pose 3 big risks to Apple, BofA warns”.

Verizon Communications (VZ) fell 10.1% to $41.65. It was its biggest one-day drop since 9 October, based on the past year of closes. The shares are up 5.0% this year and 16.9% below their 52-week closing high. Coverage since the move includes Yahoo Finance's headline “SpaceX's Starlink could pose 3 big risks to Apple, BofA warns”.

HP (HPQ) fell 6.9% to $30.20. It was its biggest one-day drop since 9 October, based on the past year of closes. The shares are up 34.1% this year and 15.8% below their 52-week closing high.

The gainers

Crown Castle (CCI) rose 15.6% to $79.64. It was its biggest one-day gain in the past year, based on the past year of closes. The shares are down 8.9% this year and 18.1% below their 52-week closing high. Coverage since the move includes TIKR's headline “Better High-Yield Dividend Stock: Crown Castle vs. Healthpeak”.

Moderna (MRNA) rose 14.2% to $225.00. It was its biggest one-day gain since 9 October, based on the past year of closes. The shares are up 625% this year and 5.0% below their 52-week closing high. Coverage since the move includes Quartz's headline “Moderna stock surges more than 600% in 2026”.

Humana (HUM) rose 11.6% to $431.87. It was its biggest one-day gain in the past year, based on the past year of closes. The shares are up 69.2% this year and at their 52-week closing high. On 9 October the company filed an 8-K in which it published a Regulation FD disclosure. Coverage since the move includes InvestorsHub's headline “DataMeds AI Secures Medicaid Coverage for ChemoFx Assay in Gynecologic Cancers”.

American Tower Corporation (REIT) (AMT) rose 9.3% to $182.24. It was its biggest one-day gain since 9 October, based on the past year of closes. The shares are up 4.0% this year and 6.0% below their 52-week closing high.

The megacaps

Of the 12 most-watched names we track, 4 closed higher. Meta (META) did best at +3.38%, and Supermicro (SMCI) worst at -4.49%.