Exhibit 99.1

NOTICE OF FULL REDEMPTION

DexCom, Inc.

June 29, 2020

Dear Note Holder:

Pursuant to that certain Indenture dated as of May 12, 2017 (the “Indenture”) between DexCom, Inc., a Delaware corporation (the “Company”), and U.S. Bank National Association, as Trustee (the “Trustee”), the Company originally issued $400,000,000 in principal amount of 0.75% Senior Convertible Notes due 2022 (the “Notes”). This letter shall serve as formal notice pursuant to Section 3.02 of the Indenture that the Company has elected to redeem in full all of the outstanding Notes on July 31, 2020 (the “Redemption Date”).

OPTIONS AVAILABLE TO HOLDERS OF NOTES

At any time prior to 5:00 p.m., New York City time, on July 30, 2020, the last business day prior to the Redemption Date, each $1,000.00 principal amount of the Notes is convertible, at the option of the holder, at the conversion price of $99.09 per share, into 10.0918 shares of the Company’s common stock (the “Common Stock”). The closing price of the Common Stock as reported on the Nasdaq Global Select Market on June 26, 2020 was $383.06 per share. Holders of Notes are urged to obtain current market quotations for the Common Stock (Nasdaq: DXCM). In the event such conversion would result in a fractional share of Common Stock, an amount equivalent to the value of the fractional share based on the closing sale price of the Common Stock on the conversion date will be paid in cash by the Company as provided in the Indenture. The Settlement Method for all Notes so converted shall be Physical Settlement.

The conversion right expires at 5:00 p.m., New York City time, on July 30, 2020 unless the Company fails to pay the Redemption Price. Any Notes which have not been properly delivered for conversion in accordance with the Indenture prior to such time will be automatically redeemed. Holders who want to convert Notes into Common Stock must satisfy the requirements set forth in the Notes and in the Indenture. The address of U.S. Bank National Association, the conversion agent for the Notes, is as follows:

U.S. Bank National Association

West Side Flats Operations Center

60 Livingston Avenue, Mail Station – EP-MN-WS2N

St Paul, MN 55107

Attn: Conversion Processing/Dexcom

Any Notes which have not been converted into Common Stock on or prior to 5:00 p.m., New York City time, on July 30, 2020 will be redeemed on the Redemption Date. Upon redemption, a holder will receive 100% of the principal amount of such holder’s Notes (the “Redemption Price”) and accrued and unpaid interest thereon to, but excluding, the Redemption Date. On and after the Redemption Date, and unless the Company defaults in the payment of the Redemption Price, interest will cease to accrue and holders of Notes will not have any rights as such holders other than the right to receive 100% of the principal amount of such holder’s Notes, without further interest, upon surrender of their Notes to U.S. Bank National Association, in its capacity as payment agent (in such capacity, the “Paying Agent”).

To receive payment of the Redemption Price and accrued and unpaid interest on the Notes to, but excluding, the Redemption Date, holders must surrender the Notes to the Paying Agent for cancellation. The address of the Paying Agent is as follows:

U.S. Bank National Association

Global Corporate Trust Services

Attn: Specialized Finance

111 Fillmore Ave. East,

EP-MN-WS2N

St. Paul, MN 55107

When inquiring about this redemption, please have the Note number available. Please inform the customer service representative of the CUSIP number of the Notes. Customer Service can be reached at (800) 934-6802.

IMPORTANT INFORMATION REGARDING TAX CERTIFICATION AND POTENTIAL WITHHOLDING:

Pursuant to U.S. federal tax laws, you have a duty to provide the applicable type of tax certification form issued by the U.S. Internal Revenue Service (“IRS”) to U.S. Bank National Association to ensure payments are reported accurately to you and to the IRS. In order to permit accurate withholding (or to prevent withholding), a complete and valid tax certification form must be received by U.S. Bank National Association before payment of the redemption proceeds is made to you. Failure to timely provide a valid tax certification form as required will result in the maximum amount of U.S. withholding tax being deducted from any redemption payment that is made to you.

QUESTIONS/FURTHER INFORMATION

If you have any questions regarding the redemption of the Notes or related matters, you may contact the following persons: