OPINION OF THE COURT
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delivered the opinion of the Court. Nearly all Americans who work for wages pay taxes on those wages un
I
A
Most doctors who graduate from medical school in the United States pursue additional education in a specialty to become board certified to practice in that field. Petitioners Mayo Foundation for Medical Education and Research, Mayo Clinic, and the Regents of the University of Minnesota (collectively Mayo) offer medical residency programs that provide
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such instruction. Mayo’s residency programs, which usually last three to five years, train doctors primarily through hands-on experience. Residents often spend between 50 and 80 hours a week caring for patients, typically examining and diagnosing them, prescribing medication, recommending plans of care, and performing certain procedures. Residents are generally supervised in this work by more senior residents and by faculty members known as attending physicians. In 2005, Mayo paid its residents annual “stipends” ranging between $41,000 and $56,000 and provided them with health insurance, malpractice insurance, and paid vacation time.
Mayo residents also take part in “a formal and structured educational program.” Brief for Petitioners 5 (internal quotation marks omitted). Residents are assigned textbooks and journal articles to read and are expected to attend weekly lectures and other conferences. Residents also take written exams and are evaluated by the attending faculty physicians. But the parties do not dispute that the bulk of residents’ time is spent caring for patients.
B
Through the Social Security Act and related legislation, Congress has created a comprehensive national insurance system that provides benefits for retired workers, disabled workers, unemployed workers, and their families. See United States v. Lee,
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Congress has, however, exempted certain categories of service and individuals from FICA’s demands. As relevant here, Congress has excluded from taxation “service performed in the employ of . . . a school, college, or university ... if such service is performed by a student who is enrolled and regularly attending classes at such school, college, or university.” § 3121(b)( 10) (2006 ed.). The Social Security Act, which governs workers’ eligibility for benefits, contains a corresponding student exception materially identical to § 3121(b)(10). 42 U.S.C. § 410(a)(10).
For its part, the Social Security Administration (SSA) also articulated in its regulations a case-by-case approach to the corresponding student exception in the Social Security Act. See 20 CFR § 404.1028(c) (1998). The SSA has, however, “always held that resident physicians are not students.” SSR 78-3, Cum. Bull. 1978, pp. 55-56. In 1998, the Court of Appeals for the Eighth Circuit held that the SSA could not categorically exclude residents from student status, given that its regulations provided for a case-by-case approach. See Minnesota v. Apfel,
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the ground that medical residents qualified as students under § 3121(b)( 10) of the Internal Revenue Code.
Facing that flood of claims, the Treasury Department “determined that it [wa]s necessary to provide additional clarification of the ter[m]” “student” as used in § 3121(b)( 10), particularly with respect to individuals who perform “services that are in the nature of on the job training.” 69 Fed. Reg. 8605 (2004). The Department proposed an amended rule for comment and held a public hearing on it. See id., at 76405.
On December 21, 2004, the Department adopted an amended rule prescribing that an employee’s service is “incident” to his studies only when “ [t]he educational aspect of the relationship between the employer and the employee, as compared to the service aspect of the relationship, [is] predominant.” Id., at 76408; Treas. Reg. § 31.3121(b)(10)-2(d)(3)(i), 26 CFR § 31.3121(b)(10)-2(d)(3)(i) (2005). The rule categorically provides that “ [t]he services of a full-time employee”—as defined by the employer’s policies, but in any event including any employee normally scheduled to work 40 hours or more per week—“are not incident to and for the purpose of pursuing a course of study.” 69 Fed. Reg. 76408; Treas. Reg. § 31.3121(b)(10)-2(d)(3)(iii), 26 CFR § 31.3121(b)(10)-2(d)(3)(iii) (the full-time employee rule). The amend ed provision clarifies that the Department’s analysis “is not affected by the fact that the services performed . . . may have an educational, instructional, or training aspect.” Ibid. The rule also includes as an example the case of “Employee E,” who is employed by “University V” as a medical resident. 69 Fed. Reg. 76409; Treas. Reg. § 31.3121(b)(10)-2(e), 26 CFR § 31.3121(b)(10)-2(e) (Example 4). Because Employee E’s “normal work schedule calls for [him] to perform services 40 or more hours per week,” the rule provides that his service is
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69 Fed. Reg. 76409, 76410; Treas. Reg. § 31.3121(b)(10)-2(e), 26 CFR § 31.3121(b)( 10)—2(e) (Example 4).
C
After the Department promulgated the full-time employee rule, Mayo filed suit seeking a refund of the money it had withheld and paid on its residents’ stipends during the second quarter of 2005.
The District Court granted Mayo’s motion for summary judgment. The court held that the full-time employee rule is inconsistent with the unambiguous text of § 3121, which the court understood to dictate that “an employee is a ‘student’ so long as the educational aspect of his service predominates over the service aspect of the relationship with his employer.”
The Government appealed, and the Court of Appeals reversed.
We granted Mayo’s petition for certiorari.
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II
A
We begin our analysis with the first step of the two-part framework announced in Chevron, supra, at 842-843,
Mayo nonetheless contends that the Treasury Department’s full-time employee rule must be rejected under Chevron step one. Mayo argues that the dictionary definition of “student”—one “who engages in ‘study’ by applying the mind ‘to the acquisition of learning, whether by means of books, observation, or experiment’ ”— plainly encompasses residents. Brief for Petitioners 22 (quoting Oxford Universal Dictionary 2049-2050 (3d ed. 1955)). And, Mayo adds, residents are not excluded from that category by the only limitation on students Congress has imposed under the statute—that they “be ‘enrolled and regu
Mayo’s reading does not eliminate the statute’s ambiguity as applied to working professionals. In its reply brief, Mayo acknowledges that a full-time professor taking evening classes—a person who presumably would satisfy the statute’s class-enrollment requirement and apply his mind to learning—could be excluded from the exemption and taxed because he is not “ ‘predominantly]’ ” a student. Reply Brief for Petitioners 7. Medical residents might likewise be excluded on the same basis; the statute itself does not resolve the ambiguity.
The District Court interpreted § 3121(b)( 10) as unambiguously foreclosing the Department’s rule by mandating that
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an employee be deemed “a ‘student’ so long as the educational aspect of his service predominates over the service aspect of the relationship with his employer.”
To the extent Congress has specifically addressed medical residents in §3121, moreover, it has expressly excluded these doctors from exemptions they might otherwise invoke. See §§ 3121(b)(6)(B), (7)(C)(ii) (excluding medical residents from exemptions available to employees of the District of Columbia and the United States). That choice casts doubt on any claim that Congress specifically intended to insulate medical residents from FICA’s reach in the first place.
In sum, neither the plain text of the statute nor the District Court’s interpretation of the exemption “speak[s] with the precision necessary to say definitively whether [the statute] applies to” medical residents. United States v. Eurodif S. A.,
B
In the typical case, such an ambiguity would lead us inexorably to Chevron step two, under which we may not disturb an agency rule unless it is “ ‘arbitrary or capricious in substance, or manifestly contrary to the statute.’ ” Household Credit Services, Inc. v. Pfennig,
Mayo asks us to apply the multifactor analysis we used to review a tax regulation in National Muffler, supra. There we explained:
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“A regulation may have particular force if it is a substantially contemporaneous construction of the statute by those presumed to have been aware of congressional intent. If the regulation dates from a later period, the manner in which it evolved merits inquiry. Other relevant considerations are the length of time the regulation has been in effect, the reliance placed on it, the consistency of the Commissioner’s inter*598 pretation, and the degree of scrutiny Congress has devoted to the regulation during subsequent reenactments of the statute.” Id., at 477,99 S. Ct. 1304 ,59 L. Ed. 2d 519 .
The Government, on the other hand, contends that the National Muffler standard has been superseded by Chevron. The sole question for the Court at step two under the Chevron analysis is “whether the agency’s answer is based on a permissible construction of the statute.”
Since deciding Chevron, we have cited both National Muffler and Chevron in our review of Treasury Department regulations. See, e.g., United States v. Cleveland Indians Baseball Co.,
Although we have not thus far distinguished between National Muffler and Chevron, they call for different analyses of an ambiguous statute. Under National Muffler, for example, a court might view an agency’s interpretation of a statute with heightened skepticism when it has not been consistent over time, when it was promulgated years after the relevant statute was enacted, or because of the way in which the regulation evolved.
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decision. See
Under Chevron, in contrast, deference to an agency’s interpretation of an ambiguous statute does not turn on such considerations. We have repeatedly held that “[algency inconsistency is not a basis for declining to analyze the agency’s interpretation under the Chevron framework.” National Cable & Telecommunications Assn. v. Brand X Internet Services,
Aside from our past citation of National Muffler, Mayo has not advanced any justification for applying a less deferential standard of review to Treasury Department regulations than we apply to the rules of any other agency. In the absence of such justification, we are not inclined to carve out an approach to administra
The principles underlying our decision in Chevron apply with full force in the tax context. Chevron recognized that “[t]he power of an administrative agency to administer a congressionally
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created . . . program necessarily requires the formulation of policy and the making of rules to fill any gap left, implicitly or explicitly, by Congress.”
As one of Mayo’s amici points out, however, both the full-time employee rule and the rule at issue in National Muffler were promulgated pursuant to the Treasury Department’s general authority under 26 U.S.C. § 7805(a) to “prescribe all needful rules and regulations for the enforcement” of the Internal Revenue Code. See Brief for Carlton M. Smith 4-7. In two decisions predating Chevron, this Court stated that “we owe the [Treasury Department’s] interpretation less deference” when it is contained in a rule adopted under that “general authority” than when it is “issued under a specific grant of authority to define a statutory term or prescribe a method of executing a statutory provision.” Rowan Cos. v. United States,
Since Rowan and Vogel were decided, however, the administrative landscape has changed significantly. We have held
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that Chevron deference is appropriate “when it appears that Congress delegated authority to the agency generally to make rules carrying the force of law, and that the agency interpretation claiming deference was promulgated in the exercise of that authority.” Mead,
We believe Chevron and Mead, rather than National Muffler and Rowan, provide the appropriate framework for evaluating the full-time employee rule. The Department issued the full-time employee rule pursuant to the explicit authorization to “prescribe all needful rules and regulations for the enforcement” of the Internal Revenue Code. 26 U.S.C. § 7805(a) (2006 ed.). We have found such “express congressional authorizations to engage in the process of rulemaking” to be “a very good indicator of delegation meriting Chevron treatment.” Mead, supra, at 229,
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Chevron deference. Mead, supra, at 230-231,
We have explained that “the ultimate question is whether Congress would have intended, and expected, courts to treat [the regulation] as within, or outside, its delegation to the agency of ‘gap-filling’ authority.” Id., at 173,
C
The full-time employee rule easily satisfies the second step of Chevron, which asks whether the Department’s rule is a “reasonable interpretation” of the enacted text.
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inquiry into “what [each] employee does [in his service] and why” he does it. Id., at 7. Mayo also objects that the Department has drawn an arbitrary distinction between “hands-on training” and “classroom instruction.” Brief for Petitioners 35.
We disagree. Regulation, like legislation, often requires drawing lines. Mayo does not dispute that the Treasury Department reasonably sought a way to distinguish between workers who study and students who work, see IRS Letter Ruling 9332005 (May 3, 1993). Focusing on the hours an individual works and the hours he spends in studies is a perfectly sensible way of accomplishing that goal. The Department explained that an individual’s service and his “course of study are separate and distinct activities” in “the vast majority of cases,” and reasoned that “[e]mployees who are working enough hours to be considered full-time employees . . . have filled the conventional measure of available time with work, and not study.” 69 Fed. Reg. 8607. The Department thus did not distinguish classroom education from clinical training but rather education from service. The Department reasonably concluded that its full-time employee rule would “improve administrability,” id., at 76405, and it thereby “has avoided the wasteful litigation and continuing uncertainty that would inevitably accompany any purely case-by-case approach” like the one Mayo advocates, United States v. Cornell,
As the Treasury Department has explained, moreover, the full-time employee rule has more to recommend it than administrative convenience. The Department reasonably determined that taxing residents under FICA would further the purpose of the Social Security Act and comport with this Court’s precedent. As the Treasury Department appreciated, this Court has understood the terms of the Social Security Act to “ ‘import a breadth of coverage,’ ” 69 Fed. Reg. 8605 (quoting Social Security Bd. v. Nierotko,
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taxation are to be construed narrowly,” Bingler v. Johnson,
The Department’s rule takes into account the SSA’s concern that exempting residents from FICA would deprive residents and their families of vital disability and survivorship benefits that Social Security provides. Id., at 8605. Mayo wonders whether the
We do not doubt that Mayo’s residents are engaged in a valuable educational pursuit or that they are students of their craft. The question whether they are “students” for purposes of § 3121, however, is a different matter. Because it is one to which Congress has not directly spoken, and because the Treasury Department’s rule is a reasonable construction of what Congress has said, the judgment of the Court of Appeals must be affirmed.
It is so ordered.
Justice Kagan took no part in the consideration or decision of this case.
