T-Mobile US
T-Mobile confirmed unauthorized access to its data and later identified tens of millions of current, former and prospective customers in stolen files.
-11.1% TMUS vs +0.3% SPY
This site shows how share prices moved after an incident became public. It does not prove that the incident caused the move. Company news, sector moves and the wider market can affect every result. Educational only — not investment advice.
Disclosure timing
When could the market react?
The baseline is the last adjusted close before the news was public. The reaction session is the first close afterward.
- 01Baseline sessionAug 13, 2021
Normalized to 100 for both TMUS and SPY.
- 02Public disclosureAug 16, 2021 · time unknown
Publication time is not documented; lower timing precision.
- 03First reaction closeAug 16, 2021
-2.9% company total return versus +0.2% for SPY; -3.1 pp market-relative return.
Disclosure time is unknown; the previous session close is used as baseline.
Time windows
Company vs SPY
Each row uses the last trading session on or before its target date. “Market-relative” is the company return minus the SPY return, in percentage points.
| Window | Endpoint | TMUS | SPY | Market-relative | Signal |
|---|---|---|---|---|---|
| First reaction | Aug 16, 2021 | -2.9% | +0.2% | -3.1 pp | Below SPY |
| +7 days | Aug 23, 2021 | -1.7% | +0.3% | -2.0 pp | Below SPY |
| +1 month | Sep 16, 2021 | -11.1% | +0.3% | -11.3 pp | Below SPY |
| +3 months | Nov 16, 2021 | -18.3% | +5.6% | -23.9 pp | Below SPY |
| +6 months | Feb 16, 2022 | -12.1% | +0.8% | -12.9 pp | Below SPY |
| +12 months | Aug 16, 2022 | +1.2% | -2.3% | +3.4 pp | Above SPY |
Compare with current catalog aggregates
| Window | This case | Catalog median | Catalog mean | n |
|---|---|---|---|---|
| First reaction | -3.1 pp | -0.8 pp | -1.5 pp | 30 |
| +7 days | -2.0 pp | -2.0 pp | -4.0 pp | 30 |
| +1 month | -11.3 pp | -6.6 pp | -6.8 pp | 30 |
| +3 months | -23.9 pp | -5.1 pp | -6.6 pp | 30 |
| +6 months | -12.9 pp | -5.6 pp | -7.5 pp | 30 |
| +12 months | +3.4 pp | -3.7 pp | -10.1 pp | 30 |
Normalized total return
TMUS compared with SPY
Baseline session = 100. Adjusted close reflects splits and reinvested distributions.
T-Mobile US had +1.2% company total return versus -2.3% for SPY; +3.4 pp market-relative return. The chart shows normalized adjusted-close performance for up to 24 months.
View tabular chart fallback
| Date | TMUS | SPY |
|---|---|---|
| Aug 13, 2021 | 100.0 | 100.0 |
| Sep 14, 2021 | 88.9 | 99.6 |
| Oct 13, 2021 | 80.3 | 97.9 |
| Nov 11, 2021 | 81.7 | 104.3 |
| Dec 13, 2021 | 79.3 | 105.0 |
| Jan 12, 2022 | 76.5 | 106.3 |
| Feb 11, 2022 | 85.9 | 99.4 |
| Mar 15, 2022 | 87.1 | 96.2 |
| Apr 13, 2022 | 93.0 | 100.4 |
| May 13, 2022 | 87.2 | 91.0 |
| Jun 14, 2022 | 86.2 | 84.7 |
| Jul 15, 2022 | 94.8 | 87.6 |
| Aug 15, 2022 | 101.2 | 97.5 |
| Sep 14, 2022 | 97.9 | 89.7 |
| Oct 13, 2022 | 91.8 | 83.6 |
| Nov 11, 2022 | 100.9 | 91.0 |
| Dec 13, 2022 | 97.0 | 91.8 |
| Jan 13, 2023 | 103.3 | 91.4 |
| Feb 14, 2023 | 101.8 | 94.7 |
| Mar 16, 2023 | 97.6 | 90.9 |
| Apr 17, 2023 | 103.8 | 95.3 |
| May 16, 2023 | 99.1 | 94.5 |
| Jun 15, 2023 | 91.6 | 101.9 |
| Jul 18, 2023 | 95.5 | 105.0 |
| Aug 16, 2023 | 95.4 | 101.6 |
Price recovery
Recovered
Here, recovery only means that adjusted close reached the baseline again. It does not mean every effect of the incident ended.
- State
- Recovered
- Initial trough
- -3.5% on Aug 18, 2021
- Recovery close
- Aug 9, 2022
- Calendar days
- 358
- Observation cap
- 24 months after disclosure
Hypothetical $1,000
What would $1,000 have looked like?
Compare $1,000 in TMUS with $1,000 in SPY, bought and measured on the same dates.
Entry Aug 19, 2021 Exit Feb 18, 2022
Uses fractional shares and adjusted close. Leaves out taxes, fees and slippage. The holding period starts on the purchase date. This is a historical illustration, not an investment strategy.
Case note
T-Mobile initially confirmed that unauthorized access had occurred while its investigation was continuing. The following updates identified personal information in stolen files covering millions of current, former and prospective customers.
The first issuer confirmation anchors the event date. Because the retained statement does not expose a reliable release time, the previous session close is used and the precision warning remains visible on the case page.
Evidence
Sources and case review
We qualify each case before checking its price results. These links support the disclosure date, listing, incident and business impact.
- primary Aug 16, 2021T-Mobile cybersecurity incident update T-Mobile US Supports: Disclosure, Listing, Description
- primary Aug 17, 2021T-Mobile shares updated information regarding cyberattack T-Mobile US Supports: Impact, Description
- Listing evidenceChecked Jul 20, 2026T-Mobile cybersecurity incident update T-Mobile US The event-period issuer statement and SEC history confirm T-Mobile's Nasdaq listing under TMUS.
Why it is included. T-Mobile was the direct victim, confirmed the disclosure date and subsequently quantified stolen data involving a very large population and sensitive identifiers. Reviewed Jul 20, 2026.