Title 26Internal Revenue CodeRelease 119-73

§15 Effect of changes

Title 26 › Subtitle Subtitle A— - Income Taxes › Chapter CHAPTER 1— - NORMAL TAXES AND SURTAXES › Subchapter Subchapter A— - Determination of Tax Liability › Part PART III— - CHANGES IN RATES DURING A TAXABLE YEAR › § 15

Last updated Apr 6, 2026|Official source

Summary

When a tax rate changes partway through your tax year (and the change is not on the first day), figure the tax by making two tax amounts: one using the old rate on the whole year’s taxable income, and one using the new rate on the whole year’s taxable income. Then multiply each amount by the fraction of days in the year before and after the change and add them. If a tax is repealed, treat that as a rate change and use zero for the period after repeal. If a law says the change applies to years “beginning after” or “ending after” a date, the change starts the next day. If it says “beginning on or after” a date, the change starts that date. If the highest tax rate changes, any place that refers to that highest rate (except where a tax is set by referring to it) must use a weighted average of the old and new highest rates based on days before and after the change. These rules do not apply to changes under subsection (f) of section 1 (inflation adjustments) or subsection (i) of section 1 (rate reductions after 2000).

Full Legal Text

Title 26, §15

Internal Revenue Code — Source: USLM XML via OLRC

(a)If any rate of tax imposed by this chapter changes, and if the taxable year includes the effective date of the change (unless that date is the first day of the taxable year), then—
(1)tentative taxes shall be computed by applying the rate for the period before the effective date of the change, and the rate for the period on and after such date, to the taxable income for the entire taxable year; and
(2)the tax for such taxable year shall be the sum of that proportion of each tentative tax which the number of days in each period bears to the number of days in the entire taxable year.
(b)For purposes of subsection (a)—
(1)if a tax is repealed, the repeal shall be considered a change of rate; and
(2)the rate for the period after the repeal shall be zero.
(c)For purposes of subsections (a) and (b)—
(1)if the rate changes for taxable years “beginning after” or “ending after” a certain date, the following day shall be considered the effective date of the change; and
(2)if a rate changes for taxable years “beginning on or after” a certain date, that date shall be considered the effective date of the change.
(d)This section shall not apply to any change in rates under subsection (f) of section 1 (relating to adjustments in tax tables so that inflation will not result in tax increases).
(e)If the change referred to in subsection (a) involves a change in the highest rate of tax imposed by section 1 or 11(b), any reference in this chapter to such highest rate (other than in a provision imposing a tax by reference to such rate) shall be treated as a reference to the weighted average of the highest rates before and after the change determined on the basis of the respective portions of the taxable year before the date of the change and on or after the date of the change.
(f)This section shall not apply to any change in rates under subsection (i) of section 1 (relating to rate reductions after 2000).

Legislative History

Notes & Related Subsidiaries

Editorial Notes

Amendments

2001—Subsec. (f). Pub. L. 107–16, § 101(c)(3), added subsec. (f). 1988—Subsec. (e). Pub. L. 100–647 added subsec. (e). 1986—Subsec. (d). Pub. L. 99–514 amended subsec. (d) generally, substituting “apply to inflation adjustments” for “apply to section 1 rate changes made by Economic Recovery Tax Act of 1981” in heading and struck out “section 1 attributable to the

Amendments

made by section 101 of the Economic Tax Act of 1981 or” before “subsection (f)” in text. 1984—Pub. L. 98–369 renumbered section 21 of this title as this section. 1981—Subsec. (d). Pub. L. 97–34 substituted provisions that this section shall not apply to any change in rates under section 1 attributable to the

Amendments

made by section 101 of the Economic Recovery Tax Act of 1981 or subsec. (f) of section 1 for provisions that had related to the changes made by section 303(b) of the Tax Reduction Act of 1975 in the surtax exemption. Subsecs. (e), (f). Pub. L. 97–34 struck out subsecs. (e) and (f) which had related, respectively, to changes made by the Tax Reduction and Simplification Act of 1977 and to changes made by Revenue Act of 1978. 1978—Subsec. (f). Pub. L. 95–600 added subsec. (f). 1977—Subsec. (d). Pub. L. 95–30, § 101(d)(2)(A), (B), redesignated subsec. (f) as (d). Former subsec. (d), which directed that, in applying subsec. (a) to a taxable year of an individual which was not a calendar year, each change made by the Tax Reform Act of 1969 in part I or in the application of part IV or V of subchapter B for purposes of the determination of taxable income should be treated as a change in a rate of tax, was struck out. Subsec. (e). Pub. L. 95–30, § 101(d)(2)(A), (C), added subsec. (e). Former subsec. (e), which directed that, in applying subsec. (a) to a taxable year of an individual which was not a calendar year, each change made by the Revenue Act of 1971 in section 141 (relating to the standard deduction) and section 151 (relating to personal exemptions) should be treated as a change in a rate of tax, was struck out. Subsec. (f). Pub. L. 95–30, § 101(d)(2)(B), redesignated subsec. (f) as (d). 1976—Subsec. (f). Pub. L. 94–455 substituted “in the surtax exemption and any change under section 11(d) in the surtax exemption” for “and the change made by section 3(c) of the Revenue Adjustment Act of 1975 in section 11(d) (relating to corporate surtax exemption)”. 1975—Subsec. (f). Pub. L. 94–164 inserted reference to change made by section 3(c) of the Revenue Adjustment Act of 1975. Pub. L. 94–12 added subsec. (f). 1971—Subsec. (e). Pub. L. 92–178 added subsec. (e). 1969—Subsec. (d). Pub. L. 91–172 substituted provisions covering changes made by the Tax Reform Act of 1969 in case of individuals for provisions covering changes made by Revenue Act of 1964. 1964—Subsec. (d). Pub. L. 88–272 amended subsection generally by substituting provisions relating to changes made by the Revenue Act of 1964, for provisions relating to taxable years beginning before Jan. 1, 1954, and ending after Dec. 31, 1953.

Statutory Notes and Related Subsidiaries

Effective Date

of 2001 AmendmentAmendment by Pub. L. 107–16 applicable to taxable years beginning after Dec. 31, 2000, see section 101(d)(1) of Pub. L. 107–16, set out as an Effective and Termination Dates of 2001 Amendment note under section 1 of this title.

Effective Date

of 1988 AmendmentAmendment by Pub. L. 100–647 effective, except as otherwise provided, as if included in the provision of the Tax Reform Act of 1986, Pub. L. 99–514, to which such amendment relates, see section 1019(a) of Pub. L. 100–647, set out as a note under section 1 of this title.

Effective Date

of 1986 AmendmentAmendment by Pub. L. 99–514 applicable to taxable years beginning after Dec. 31, 1986, see section 151(a) of Pub. L. 99–514, set out as a note under section 1 of this title.

Effective Date

of 1981 AmendmentAmendment by Pub. L. 97–34 applicable to taxable years beginning after Dec. 31, 1981, see section 101(f)(1) of Pub. L. 97–34, set out as a note under section 1 of this title.

Effective Date

of 1977 AmendmentAmendment by Pub. L. 95–30 applicable to taxable years beginning after Dec. 31, 1976, see section 106(a) of Pub. L. 95–30, set out as a note under section 1 of this title.

Effective Date

of 1976 AmendmentAmendment by Pub. L. 94–455 applicable with respect to taxable years ending after Dec. 31, 1975, see section 901(d) of Pub. L. 94–455, set out as a note under section 11 of this title.

Effective Date

of 1975 AmendmentAmendment by Pub. L. 94–164 applicable to taxable years beginning after Dec. 31, 1975, see section 4(e) of Pub. L. 94–164, set out as an Effective and Termination Dates of 1975

Amendments

note under section 11 of this title.

Effective Date

of 1964 Amendment Pub. L. 88–272, title I, § 132, Feb. 26, 1964, 78 Stat. 30, provided that the amendment made by that section is effective with respect to taxable years ending after Dec. 31, 1963. Coordination of 2025 Amendment With section 15 Pub. L. 119–21, title VII, § 70001(b), July 4, 2025, 139 Stat. 158, provided that: “section 15 of the Internal Revenue Code of 1986 shall not apply to any change in rate of tax by reason of any provision of, or amendment made by, this title [see Tables for classification].” Coordination of 2017 Amendment With section 15This section not to apply to any change in a rate of tax by reason of section 1(j) of this title, as added by Pub. L. 115–97, see section 1(j)(6) of this title. Coordination of 1997 Amendment With section 15 Pub. L. 105–34, title I, § 1(c), Aug. 5, 1997, 111 Stat. 788, provided that: “No amendment made by this Act [see Tables for classification] shall be treated as a change in a rate of tax for purposes of section 15 of the Internal Revenue Code of 1986.” Coordination of 1993 Amendment With section 15 Pub. L. 103–66, title XIII, § 13001(c), Aug. 10, 1993, 107 Stat. 416, provided that: “Except in the case of the

Amendments

made by section 13221 [amending section 11, 852, 1201, and 1445 of this title] (relating to corporate rate increase), no amendment made by this chapter [chapter 1 (§§ 13001–13444) of title XIII of Pub. L. 103–66, see Tables for classification] shall be treated as a change in a rate of tax for purposes of section 15 of the Internal Revenue Code of 1986.” Coordination of 1990 Amendment With section 15 Pub. L. 101–508, title XI, § 11001(c), Nov. 5, 1990, 104 Stat. 1388–400, provided that: “Except as otherwise expressly provided in this title, no amendment made by this title [see Tables for classification] shall be treated as a change in a rate of tax for purposes of section 15 of the Internal Revenue Code of 1986.” Coordination of 1987 Amendment With section 15 Pub. L. 100–203, title X, § 10000(c), Dec. 22, 1987, 101 Stat. 1330–382, provided that: “No amendment made by this title [see Tables for classification] shall be treated as a change in a rate of tax for purposes [of] section 15 of the Internal Revenue Code of 1986.” Coordination of 1986 Amendment With section 15 Pub. L. 99–514, § 3(b), Oct. 22, 1986, 100 Stat. 2095, provided that: “(1) In general.—Except as provided in paragraph (2), for purposes of section 15 of the Internal Revenue Code of 1986, no amendment or repeal made by this Act [see Tables for classification] shall be treated as a change in the rate of a tax imposed by chapter 1 of such Code. “(2) Exception.—Paragraph (1) shall not apply to the amendment made by section 601 [amending section 11 of this title] (relating to corporate rate reductions).”

Reference

Citations & Metadata

Citation

26 U.S.C. § 15

Title 26Internal Revenue Code

Last Updated

Apr 6, 2026

Release point: 119-73