3Q21 Supplemental

Table of Contents

Overview
Earnings Release	3
Company Profile	7
Summary of Financial Data	8
Financial Statements
Consolidated Balance Sheets	9
Consolidated Statements of Operations	10
Reconciliations of Net Income to FFO, AFFO, EBITDAre and Adjusted EBITDA	11
Operating Portfolio
Operating Portfolio & 10 Largest Customers	12
Leasing Statistics	13
Geographic and Vertical Diversification	15
Development
Capital Expenditures and Completed Pre-Stabilized Projects	16
Development Summary	17
Capital Structure
Market Capitalization and Debt Summary	18
Interest Summary, Debt Covenants and Liquidity	19
Components of Net Asset Value	20
2021 Guidance	21
Appendix	22

Quarter Ended September 30, 2021

Overview	Financial	Operating	Development	Capital	Components	Guidance	Appendix	2
Statements	Portfolio	Structure	of NAV

CoreSite Reports Third Quarter 2021 Financial Results

- Delivered Strong Q3 Financial Results, Including 6.4% Revenue Growth Year Over Year -

DENVER, CO - October 28, 2021 - CoreSite Realty Corporation (NYSE:COR) ("the Company"), a premier provider of secure, reliable, high-uptime data center campuses with high-performance cloud access and interconnection solutions across the U.S., today announced financial results for the quarter ended September 30, 2021.

Q3 2021 Quarterly Highlights

1. Key Financial Results -

1. Grew operating revenues to $163.9 million, an increase of 6.4% year over year and 1.1% sequentially

1. Delivered net income of $0.50 per common diluted share, consistent year over year and a decrease of $0.09 sequentially

1. Grew adjusted EBITDA to $85.7 million, an increase of 5.2% year over year and a decrease of 2.0% sequentially o Generated FFO of $1.39 per diluted share and unit, an increase of $0.06, or 4.5% year over year, and a decrease
   of $0.03, or 2.1% sequentially
   o Paid a dividend of $1.27 per share for the third quarter on October 15th, consistent with the prior quarter

1. Lease Commencements -

1. Commenced 122 new and expansion leases for 29,308 net rentable square feet ("NRSF"), representing $7.1

million of annualized GAAP rent, for an average rate of $242 per NRSF

1. LA3 Phase 1 was 93% leased and moved into the stabilized data center portfolio less than 12 months after being placed into service

1. Leasing Activity -

1. Signed 122 new and expansion leases for $7.2 million of annualized GAAP rent during the third quarter, and signed a large scale lease for $1.7 million of annualized GAAP rent at SV7 on October 7th, representing total

leasing activity of $8.9 million of annualized GAAP rent

1. This $8.9 million of annualized GAAP rent reflects 62,098 NRSF for an average rate of $143 per NRSF and includes leases signed at SV7 for $2.9 million of annualized GAAP rent

1. Renewed 296 leases for 118,887 NRSF and $18.7 million of annualized GAAP rent, for an average rate of $157 per NRSF

1. Renewed leases reflected an increase of 2.0% in cash rent and 5.7% in GAAP rent, and we reported churn of 2.5%

"Demand trends continue to be positive for low-latency,high-performance,hybrid-cloud IT solutions across our markets," said Paul Szurek, CoreSite's President and Chief Executive Officer. "Our excellent team continues to build on and strengthen the diverse customer ecosystems in each of our eight markets and our connectivity products to facilitate digital transformation. Our purpose-built, power efficient and scalable data center campuses enable the interoperability required for multi and hybrid-cloud solutions the current and future needs of enterprises, networks and cloud providers."

Quarter Ended September 30, 2021

Overview	Financial	Operating	Development	Capital	Components	Guidance	Appendix	3
Statements	Portfolio	Structure	of NAV

Quarter Ended September 30, 2021

Sales Activity

CoreSite signed new and expansion leases of $7.2 million in annualized GAAP rent during the third quarter, and signed a large scale lease for $1.7 million of annualized GAAP rent at SV7 on October 7th, representing total leasing activity of $8.9 million of annualized GAAP rent.

"We are encouraged by our continuing strong attraction of retail and small scale leases, which are fundamental to our go-to-market strategy," said Steve Smith, CoreSite's Chief Revenue Officer. "We are focused on continual generation of profitable organic growth, attracting high-quality new logos, and creating incremental value to our customers and shareholders through the lease-up of our available capacity within our portfolio."

Including the $1.7 million of annualized GAAP rent for the scale lease signed on October 7th, CoreSite had annualized GAAP backlog of $9.9 million, or $17.2 million on a cash basis, for leases signed but not yet commenced. The difference between GAAP and cash backlog is primarily driven by a handful of scale leases with power ramps during the early portion of their lease terms.

Other Financial Results

CoreSite's $163.9 million of operating revenues for the third quarter, included $138.1 million of rental, power and related revenue, reflecting 6.0% year over year growth, $23.0 million of interconnection revenue, reflecting 8.7% year over year growth, and $2.8 million of office, light-industrial and other revenue. Net income was $24.1 million for the quarter, or $0.50 attributable to each common diluted share.

Development Activity

CoreSite continues to develop new capacity as needed to meet market demand.

1. The LA3 Phase 2 development project, comprised of 54,000 NRSF and 6 megawatts ("MW"), was completed in

October. As of September 30, 2021, LA3 Phase 2 was approximately 8% leased.

1. NY2 Phase 4A, comprised of 35,000 NRSF and 4 MWs, is under construction and is on track for its estimated completion in the first quarter of 2022.

CoreSite's ongoing data center development and operational position includes -

1. the ability to increase its occupied footprint of purpose-built data centers, both owned and leased, by approximately 2.0 million NRSF, or about 84.0%, including space unoccupied, under construction, pre- construction design and permitting or held for development, and

1. owning (versus leasing) 93.1% of its current and developable 4.3 million data center NRSF, supporting operational control, expansion and long-term expense management.

Balance Sheet and Liquidity

The Company's balance sheet reflects a ratio of net principal debt to second quarter annualized adjusted EBITDA of

5.2 times, or 5.1 times including GAAP backlog. As of the end of the third quarter, CoreSite had approximately $235.4 million of current liquidity, including $3.4 million of cash and $231.9 million of available capacity on its revolving credit facility.

Updated 2021 Guidance

CoreSite updated its 2021 guidance related to total capital expenditures to its new guidance range of $140 million to $150 million from its previous range of $185 million to $225 million. CoreSite's full 2021 guidance can be found in the Company's third quarter 2021 Supplemental Earnings Information on page 21.

Quarter Ended September 30, 2021

Overview	Financial	Operating	Development	Capital	Components	Guidance	Appendix	4
Statements	Portfolio	Structure	of NAV

Quarter Ended September 30, 2021

Conference Call Details

CoreSite will host its third quarter 2021 earnings call on Thursday, October 28, 2021, at 12:00 p.m. (Eastern Time). The call will be accessible by dialing 1-877-407-3982 (domestic) or 1-201-493-6780 (international).

A replay will be available after the call until November 4, 2021, and can be accessed dialing 1-844-512-2921 (domestic) or 1-412-317-6671 (international). The passcode for the replay is 13723625.

The quarterly conference call also will be offered as a simultaneous webcast, accessible by visiting CoreSite.com and clicking on the "Investors" link. An on-line replay will be available for a limited time immediately following the call.

Concurrently with issuing its financial results, the Company will post its third quarter 2021 Supplemental Information on its website at CoreSite.com, under the "Investors" link.

Upcoming Conferences and Events

CoreSite's management will participate in the Nareit REITworld Virtual Conference on November 9th.

About CoreSite

CoreSite Realty Corporation (NYSE:COR) delivers secure, reliable, high-uptime data center campuses with high- performance cloud access and interconnection solutions to a growing customer ecosystem across eight key North American markets. More than 1,370 of the world's leading enterprises, network operators, cloud providers, and supporting service providers choose CoreSite to connect, protect and optimize their performance-sensitive data, applications and computing workloads. Our scalable, flexible solutions and 480+ dedicated employees consistently deliver unmatched data center options - all of which leads to a best-in-class customer experience and lasting relationships. For more information, visit www.CoreSite.com.

CoreSite Contact

Kate Ruppe

Investor Relations Manager [e-mail]

Quarter Ended September 30, 2021

Overview	Financial	Operating	Development	Capital	Components	Guidance	Appendix	5
Statements	Portfolio	Structure	of NAV