Discount from market price (in percent)

AMERICAN TOWER CORPORATION AND SUBSIDIARIESNOTES TO CONSOLIDATED AND CONDENSED CONSOLIDATED FINANCIAL STATEMENTS(tabular amounts in millions, unless otherwise noted)when they would have been available under the CoreSite plan, or March 20, 2023, at which time they will no longer be available for grant. In addition, the Company maintains an employee stock purchase plan (the “ESPP”) pursuant to which eligible employees may purchase shares of the Company’s common stock on the last day of each bi-annual offering period at a 15% discount from the lower of the closing market value on the first or last day of such offering period. The offering periods run from June 1 through November 30 and from December 1 through May 31 of each year.During the three and nine months ended September 30, 2022 and 2021, the Company recorded the following stock-based compensation expense in selling, general, administrative and development expense: 

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|  |  | Three Months Ended September 30, |  | Nine Months Ended September 30, |
|   |  | 2022 |  | 2021 |  | 2022 |  | 2021 |
| Stock-based compensation expense |  | $ | 39.2  |  |  | $ | 28.1  |  |  | $ | 138.1  |  |  | $ | 98.0  |  |
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Stock Options—As of September 30, 2022, there was no unrecognized compensation expense related to unvested stock options.The Company’s option activity for the nine months ended September 30, 2022 was as follows (shares disclosed in full amounts):

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| --- | --- | --- | --- | --- | --- | --- | --- | --- |
|  |  |  |  |  |  |  |  |  |
|  |  | Number of Options |
| Outstanding as of January 1, 2022 |  | 1,067,999  |  |
|  |  |  |
| Exercised |  | (157,168) |  |
| Forfeited |  | —  |  |
| Expired |  | —  |  |
| Outstanding as of September 30, 2022 |  | 910,831  |  |

Restricted Stock Units—As of September 30, 2022, total unrecognized compensation expense related to unvested RSUs granted under the 2007 Plan, including the CoreSite Replacement Awards (as defined below), was $199.7 million and is expected to be recognized over a weighted average period of approximately two years. Vesting of RSUs is subject generally to the employee’s continued employment or death, disability or qualified retirement (each as defined in the applicable RSU award agreement). In December 2021, in connection with the CoreSite Acquisition, the Company assumed and converted certain equity awards previously granted by CoreSite under its equity plan into corresponding equity awards with respect to shares of the Company’s common stock (the “CoreSite Replacement Awards”). As of September 30, 2022, total unrecognized compensation expense related to the CoreSite Replacement Awards was $9.8 million and is expected to be recognized over a weighted average period of approximately one year. Performance-Based Restricted Stock Units—During the nine months ended September 30, 2022, the Company’s Compensation Committee (the “Compensation Committee”) granted an aggregate of 98,542 PSUs (the “2022 PSUs”) to its executive officers and established the performance metrics for these awards. During the years ended December 31, 2021 and 2020, the Compensation Committee granted an aggregate of 98,694 PSUs (the “2021 PSUs”) and 110,925 PSUs (the “2020 PSUs”), respectively, to its executive officers and established the performance metrics for these awards. During the year ended December 31, 2020, in connection with the retirement of the Company’s former Chief Executive Officer, an aggregate of 40,186 shares underlying the 2020 PSUs were forfeited, which included the target number of shares issuable at the end of the three-year performance period for such executive’s 2020 PSUs. Threshold, target and maximum parameters were established for the metrics for a three-year performance period with respect to each of the 2022 PSUs, the 2021 PSUs and the 2020 PSUs and will be used to calculate the number of shares that will be issuable when each award vests, which may range from zero to 200% of the target amounts. At the end of each three-year performance period, the number of shares that vest will depend on the degree of achievement against the pre-established performance goals. PSUs will be paid out in common stock at the end of each performance period, subject generally to the executive’s continued employment or death, disability or qualified retirement (each as defined in the applicable PSU award agreement). PSUs will accrue dividend equivalents prior to vesting, which will be paid out only in respect of shares that actually vest. 19
