UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 10-D

ASSET-BACKED ISSUER

DISTRIBUTION REPORT PURSUANT TO SECTION 13 OR 15(d) OF

THE SECURITIES EXCHANGE ACT OF 1934

For the monthly distribution period from August 1, 2025 to August 31, 2025

Commission File Number of issuing entity: 333-228379-11

Central Index Key Number of issuing entity: 0001867436

CarMax Auto Owner Trust 2021-3

(Exact name of issuing entity as specified in its charter)

Commission File Number of depositor: 333-228379

Central Index Key Number of depositor: 0001259380

CarMax Auto Funding LLC

(Exact name of depositor as specified in its charter)

Central Index Key Number of sponsor (if applicable): 0001601902

CarMax Business Services, LLC

(Exact name of sponsor as specified in its charter)

Greg Dostich, Vice President and Treasurer (804) 935-4512

(Name and telephone number, including area code, of the person to contact in connection with this filing)

Delaware

(State or other jurisdiction of incorporation or organization of the issuing entity)

86-6744107

(I.R.S. Employer Identification No.)

c/o CarMax Auto Funding LLC

12800 Tuckahoe Creek Parkway, Suite 400, Richmond, Virginia 23238

(Address of principal executive offices of issuing entity) (Zip Code)

(804) 935-4512

(Telephone number, including area code)

Not Applicable

(Former name, former address, if changed since last report)

Registered/reporting pursuant to (check one)

Title of Class

Section 12(b)

Section 12(g)

Section 15(d)

Name of exchange
(If Section 12(b))

Class A-1 Asset-backed Notes

[ ]

[X]

[ ]

Class A-2a Asset-backed Notes

[ ]

[X]

[ ]

Class A-2b Asset-backed Notes

[ ]

[X]

[ ]

Class A-3 Asset-backed Notes

[ ]

[X]

[ ]

Class A-4 Asset-backed Notes

[ ]

[X]

[ ]

Class B Asset-backed Notes

[ ]

[X]

[ ]

Class C Asset-backed Notes

[ ]

[X]

[ ]

Class D Asset-backed Notes

[ ]

[X]

[ ]

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days. Yes [X] No [ ]

PART I – DISTRIBUTION INFORMATION

Item 1. Distribution and Pool Performance Information.

Distribution and pool performance information with respect to the receivables that comprise the assets of CarMax Auto Owner Trust 2021-3 is set forth in the monthly servicer’s certificate attached as Exhibit 99.1.

Item 1A. Asset-Level Information.

The Asset Data File and Asset Related Document, filed as Exhibits 102 and 103, respectively, to the registrant's Form ABS-EE filed on September 15, 2025 under File No. 333-228379-11 are hereby incorporated by reference into this Form 10-D.

ITEM 1121(c) OF REGULATION AB. REPURCHASES AND REPLACEMENTS

No activity to report for the Collection Period as required by Item 1121(c) of Regulation AB.

Date of Most Recent Form ABS-15G Filed Pursuant to Rule 15Ga-1: February 7, 2025.

Central Index Key (CIK) of Securitizer: 0001259380.

PART II – OTHER INFORMATION

Item 10. Exhibits.

Exhibit 99.1 Monthly Servicer's Certificate for the collection period commencing August 1, 2025 and ending August 31, 2025

Exhibit 102 Asset Data File (incorporated by reference to registrant's Form ABS-EE, Registration File Number 333-228379-11, filed on September 15, 2025)

Exhibit 103 Asset Related Document (incorporated by reference to registrant's Form ABS-EE, Registration File Number 333-228379-11, filed on September 15, 2025)

Signatures

Pursuant to the requirements of the Securities and Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned thereunto duly authorized.

CARMAX AUTO OWNER TRUST 2021-3

(Issuing Entity)

By:

CARMAX BUSINESS SERVICES, LLC,

as Servicer

Date:

September 15, 2025

By:

/s/ Greg Dostich

Greg Dostich

Vice President and Treasurer

CarMax Auto Owner Trust 2021-3 10-D