26 CFR § 1.66-5 - Effective date.

---
identifier: "/us/cfr/t26/s1.66-5"
source: "ecfr"
legal_status: "authoritative_unofficial"
title: "26 CFR § 1.66-5 - Effective date."
title_number: 26
title_name: "Internal Revenue"
section_number: "1.66-5"
section_name: "Effective date."
chapter_name: "INTERNAL REVENUE SERVICE, DEPARTMENT OF THE TREASURY"
subchapter_number: "A"
subchapter_name: "INCOME TAX"
part_number: "1"
part_name: "INCOME TAXES"
positive_law: false
currency: "2026-04-05"
last_updated: "2026-04-05"
format_version: "1.1.0"
generator: "[email protected]"
authority: "26 U.S.C. 7805, unless otherwise noted."
regulatory_source: "T.D. 6500, 25 FR 11402, Nov. 26, 1960; 25 FR 14021, Dec. 21, 1960; T.D. 9989, 89 FR 17606, Mar. 11, 2024, unless otherwise noted."
cfr_part: "1"
---


# 1.66-5 Effective date.

Sections 1.66-1 through 1.66-4 are applicable on July 10, 2003. In addition, § 1.66-4 applies to any request for relief filed prior to July 10, 2003, for which the Internal Revenue Service has not issued a preliminary determination as of July 10, 2003.

[T.D. 9074, 68 FR 41070, July 10, 2003]