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Say a person was born at noon on January 1st, 2000. Under US law, what is the exact time that person legally turns 18? Is it the midnight before January 1st 2018, or the midnight after, or noon, or something else?

4 Answers 4

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In the US, the common law rule is that a year of age is completed on the day preceding the anniversary of one's birth.

Here are some citations from cases that relied on this rule:

  • "Full age in male or female is 21 years, which age is completed on the day preceding the 21st anniversary of a person's birth." State in Interest of FW 130 N.J. Super. 513 (1974) (citing Blackstone)
  • "The common law rule for computing age is that one is deemed to have reached a given age at the earliest moment of the day preceding an anniversary of birth." Fisher v. Smith, 319 F. Supp. 855 (D. Wash. 1970)
  • "The appellant did, then, reach the age of nineteen years on the day before the nineteenth anniversary of his birth" Turnbull v. Bonkowski, 419 F.2d 104 (D. Alaska 1969)

This is codified in some statutes and regulations. For example, CFR 404.102:

For the purpose of this subpart [...] You reach a particular age on the day before your birthday. For example, if your sixty-second birthday is on July 1, 1979, you became age 62 on June 30, 1979.

In Virginia, the Attorney General has confirmed that the common law rule is in effect:

a person attains his/her next year of age on the day prior to his/her birthday

In your example, barring a modification by state law, or an idiosyncratic treatment under a particular statute, the person would be deemed 18 years of age at the earliest moment of December 31, 2017.


For a bit of comparative law, contrast with the treatment in British Columbia:

A person reaches a particular age expressed in years at the start of the relevant anniversary of his or her date of birth. (Interpretation Act s. 25)

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    do you also know how the different time zones play into it? Example: illegal phone call from NY to LA :)
    – user3232
    Oct 28, 2015 at 3:51
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    Correct me if I'm wrong, but this doesn't affect drinking at the bar, buying cigarettes, etc. I wonder why the schism...
    – Brad Werth
    Oct 28, 2015 at 6:43
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    Wow, that's very interesting. I just assumed it, because where I am from they have these little signs by the door or register that say "you must be born before this day/year to buy...". I doubt one would be able to convince many establishments otherwise. Now I'm curious about whether they have a legal requirement to serve someone in that situation... I might need to make a new question to explore this further. Thanks!
    – Brad Werth
    Oct 30, 2015 at 16:13
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    Now I'm curious about whether they have a legal requirement to serve someone in that situation Typically, you can refuse service to anyone for any reason, as long as you aren't discriminating against a protected class. "People whose birthdays are tomorrow" are not a legally protected class in the US and stores would be within their rights to not even let such people inside, let alone serve them anything. Then again, age discrimination is illegal and I suppose one could argue that rule disproportionately affects 20-year-olds.
    – Patrick87
    Oct 30, 2015 at 20:52
  • @user3232: First, your birthday would be based on the time zone where you are born. An Australian could be born 18 hours before an Alaskan and have a later birthday. And for that illegal call from NY to LA your age would depend on where it goes to court. At the right place, you might be able to drink legally, walk 20 meters to a bar in another state where the time is snow hour later, and drinking alcohol might be illegal for you.
    – gnasher729
    Nov 30, 2019 at 17:31
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It depends

There are two different rules that are used in various jurisdictions and contexts in the United States for determining when one turns an age:

  • The "common law rule" says that one turns an age at the start of the day before that birthday. Under this rule, in your example, the person would turn 18 at the first minute of December 31, 2017. US common law often derives from English common law, which established this precedent about when one comes of age in the 17th century. (Nichols v. Ramsel, 86 Eng. Rep. 1072 (K.B. 1677); Herbert v. Turball, 83 Eng. Rep. 1129 (K.B. 1663)). Note that this rule is no longer in effect in England since the passage of the Family Law Reform Act of 1969 (as noted in this paper)!
  • The "birthday rule" states that one turns an age at the start of the day on the birthday. Under this rule, in your example, the person would turn 18 at the first minute of January 1, 2018. This is the rule almost universally observed by Americans outside of the context of law.
  • A hypothetical rule sometimes argued by parties to a case is one where the year is completed (and the next age is reached) at the same time of day that the person was born. Under this rule, in your example, the person would turn 18 at noon on January 1, 2018. However, no courts (that I have found) have been willing to accept this argument, under the common law principle that "the law takes no notice of fractions of a day"; "a day begun is a day done."

In most cases, legislators have not bothered to formally define "age" outside of occasional act-specific contexts, leaving it up to common law, intentionally or otherwise. However, in recent years, courts have been increasingly unwilling to apply the common law rule, abrogating it in favor of the birthday rule. There are a few frequent justifications for this:

  • Rule of lenity: In cases where defendants are accused of crimes on the day before their 18th (or other relevant) birthday, it is usually most favorable to them to consider them a juvenile, not having reached the age of majority, as they will likely face a lesser sentence. This situation is the most common reason for the age question to arrive before the courts.
  • Plain meaning rule: Given the relative obscurity of the common law rule and its inconsistency with the popular understanding of age, courts have found that legislatures did not intend for it to be applied when making references to ages.
  • Some courts have quoted Justice Holmes: "It is revolting to have no better reason for a rule of law than that so it was laid down in the time of Henry IV. It is still more revolting if the grounds upon which it was laid down have vanished long since, and the rule simply persists from blind imitation of the past."

Even if you are in a common law rule jurisdiction, it is unlikely to matter unless you find yourself in a court of law—most people or systems that you interact with will still apply the birthday rule.

What follows is an incomplete enumeration of jurisdictions and some of the evidence for the prevailing rule in those jurisdictions. At least sixteen states have at least partially adopted the birthday rule.

US Federal government: Mixed

Statutory law
  • Title 18 (Crimes and Criminal Punishment) uses birthday rule: "For the purposes of this chapter [Juvenile delinquency], a 'juvenile' is a person who has not attained his eighteenth birthday" 18 U.S.C. § 5031, with the historical note: "The phrase 'who has not attained his eighteenth birthday' was substituted for 'seventeen years of age or under' as more clearly reflecting congressional intent and administrative construction. The necessity of a definite fixing of the age of the juvenile was emphasized by Hon. Arthur J. Tuttle, United States district judge, Detroit, Mich., in a letter to the Committee on Revision of the Laws dated June 24, 1944."
Regulatory law
  • The Social Security Administration uses common law rule: "Age means how many years old you are. You reach a particular age on the day before your birthday. For example, if your sixty-second birthday is on July 1, 1979, you became age 62 on June 30, 1979." 20 CFR § 404.102

Alaska: Birthday rule

Case law
  • "The old practice of deeming a person to have achieved a given age on the day prior to his or her birthday is contrary to the popular understanding of birthdate. Moreover, it is inconsistent with the common application of other legal concepts which are dependent on the computation of an individual's age, such as the determination of juvenile status in criminal matters and the attainment of age for certain legal privileges and responsibilities like voting, consuming alcohol and driving an automobile. We decline to follow a rule which defies logical explanation and which is utterly inconsistent with popular and legal conceptions of time and birthdate." Fields v. Fairbanks North Star Borough, 818 P.2d 658 (1991)

California: Birthday rule

Statutory law
  • "A minor is an individual who is under 18 years of age. The period of minority is calculated from the first minute of the day on which the individual is born to the same minute of the corresponding day completing the period of minority." Cal. Fam. Code § 6500
Case law
  • "The statutory language of Civil Code section 26, though far from lucid, indicates the Legislature intended to adopt the 'birthday rule.' [...] Because a person is deemed [5 Cal. 4th 845] to have been born on the first minute of the day, the period of minority ends on that 'same minute' 18 years later. In other words, the period of minority terminates on the first minute of one's 18th birthday. Because the plain meaning of Civil Code section 26 indicates the Legislature intended to adopt the 'birthday rule,' we conclude section 26 abrogates the common law rule regarding age calculation." In re Harris, No. S022130 (1993). Note that the California Code was reorganized in 1994 and the Civil Code section referenced is now part of the Family Code quoted earlier.

District of Columbia: Birthday rule

Case law
  • "In the absence of any reasons supported in logic, we decline to follow a rule which defies human experience by determining age on the day preceding one's birthday. Moreover, we believe that in view of the rehabilitative purposes of our juvenile justice system, D.C.Code 1973, § 16-2301(3) should be strictly construed against the prosecution and in favor of the person being proceeded against. [...] Finally, the government argues that adoption of the New York rule for determining age will inject confusion into other areas of the District's law, including questions as to the exact time one becomes eligible to vote, legally consume intoxicants or enter into binding contractual arrangements. We do not explore the merits of this argument, however, for our decision is limited to a determination of age under [D.C. statute]. We merely hold that for purposes of that section appellee legally became eighteen years old on the day of his birthday and not the day before." United States v. Tucker, 407 A.2d 1067 (1979)

Georgia: Common law rule

Case law
  • "We agree that the common law rule is archaic. Since at least as early as 1896, the common law rule has come under strong criticism. Nevertheless, we are convinced that the legislature is the proper body for considering these issues. The application of the common law rule in this State occurred at least as early as 1930, it was applied to juvenile court jurisdiction in 1980, and it has remained unchanged by the legislature. The rule is not ambiguous, just archaic. And we have no information regarding how state and local government agencies deal with this issue on a day-to-day basis." In the Interest of A.P.S., a child, GA Ct of App No. A10A0069 (2010)

Indiana: Birthday rule

Case law
  • "The phrase 'reached thirty-six (36) years of age' has not been defined by statute. Rather than deriving its meaning from an obscure 1855 case, we interpret the phrase consistent with the ordinary meaning of the words and conclude that one 'reaches thirty-six (36) years of age' when one reaches one's thirty-sixth birthday. [...] Courts are bound to construe a statute to avoid absurd results and favor public convenience. If a person reaches a given age the day before his birthday, however, application of many statutes would have some unexpected results. We decline to interpret Ind.Code § 36-8-4-7 to operate in a manner so plainly at odds with the common operation of Indiana statutes." Bailey v Lawrence, 972 F.2d 1447 (7th Cir. 1992)

Kansas: Birthday rule

Case law
  • "The custom of Kansas has rejected the coming of age rule found in the common law. In Kansas a person reaches a certain age on the anniversary of their birth [...]" State v. Wright, 24 Kan. App. 2d 558

Maryland: Common law rule

Case law
  • "We do not believe that the affirmation of a principle which has been in existence for over three centuries and remains the law of most states can be deemed a 'pleading trap.' Such a departure from the common law is more properly the domain of the legislature. [...] Our holding today reduces petitioner’s perceived extension of three years by only one day. Practically speaking, we cannot believe that this in any way prevents the timely filing of a cause of action by an individual injured as a minor." Mason v. Baltimore Co. Bd. of Ed., 143 Md.App. 507, 515, 795 A.2d 211 (2002)

Michigan: Birthday rule

Case law
  • Michigan Supreme Court: "This Court '[has] not hesitated to examine common-law doctrines in view of changes in society’s mores, institutions, and problems, and to alter those doctrines where necessary.' Our role when doing so is 'to determine which common-law rules best serve the interests of Michigan citizens.' More particularly, our role in such circumstances is to determine the 'prevailing customs and practices of the people' in this state. [...] [The birthday rule] is consistent with this Court’s present understanding of the prevailing customs and practices of the people to determine the next year of age by anniversary of birth, not by the day preceding the anniversary of birth as at English common law. [...] We therefore take this opportunity to make clear that the common law of this state should now be understood to provide that a defendant is a juvenile for the purposes of Miller when he or she is under the age of 18, as determined by his or her anniversary of birth." People v. Woolfolk, No. 149127 (2014). The opinion of the Court of Appeals (Docket No. 312056) (affirmed by the Supreme Court) is the most thorough examination of other relevant case law on the age calculation topic that I've found.

Minnesota: Birthday rule

Case law
  • "Our conclusion is that the common-law rule is so at odds with common understanding that it should be abandoned, at least in determining when a person was under the age at which the district court gains jurisdiction over people charged with committing criminal acts." State v. Stangel, 284 N.W.2d 4 (1979)

New Hampshire: Birthday rule

Statutory law
  • "The common law rule that a person is a minor to the age of 21 is hereby abrogated. A person who has reached his eighteenth birthday is hereby declared to be of majority for all purposes, except as prohibited by the constitution of New Hampshire and of the United States." RSA 21-B:1

New Jersey: Birthday rule

Case law
  • "If, as it has been said, the logic of the coming of age rule is unassailable, the logic of our computation rule, which would skip the day of birth recognizing that few people actually have lived out the entirety of that day, is equally unassailable. Whether we compute age by the common-law method (counting the date of birth), or by our uniform method (excluding the date of birth) we are diverging from what, in fact, is real. [...] Nothing whatsoever is gained in differentiating between age and every other legal calculation by maintaining a single, practically unknown exception to the uniform rule of computation. [...] We think that a calculation method which foreshortens the protections with which we blanket infants must be discarded in favor of the uniform rule which provides an infant more than a full measure of protected status. For these reasons, we hold that the common law coming of age rule should be rejected in favor of our ordinary rules of calculation in deciding the date of the anniversary of one's birth." Patterson v. Monmouth Regional H. School, 222 N.J. Super. 448 (App. Div. 1987)

New Mexico: Birthday rule

Statutory law
  • "Any person who has reached his eighteenth birthday shall be considered to have reached his majority" NM Stat § 28-6-1 (2021)

New York: Birthday rule

Case law
  • The state court of appeals adopted a dissenting opinion from an lower court judgment: "[The common law rule is] a legal fiction which was embraced in order to aid persons whose ages were being determined and to prevent hardship or loss to such persons. I do not perceive the reasons why this legal fiction should be perpetuated in a situation which invites a reasonable departure from the rule." People v Stevenson, 23 A.D.2d 472 (1965), revd on dissenting opn below 17 N.Y.2d 682 (1966)

North Carolina: Birthday rule

Case law
  • "Since the issue of whether to apply the 'coming of age' or the 'birthday rule' needs resolution, we will undertake to resolve it. The modern 'birthday rule' is more reflective of common practice and understanding as to when a person reaches a given age. Since North Carolina courts have not expressly decided which rule applies, we hold today that the 'birthday rule' is the better approach and apply it to respondent under N.C.G.S. section 7A-608." In the Matter of Robinson, 464 S.E.2d 86 (1995).

Oregon: Birthday rule

Case law
  • The state appeals court affirmed a woman's conviction of sodomy in the third degree; she engaged with the activity with an underage victim on the day before the victim's 16th birthday. "That the Oregon legislature intended to adopt [the birthday] rule is evidenced by the legislative commentary to the general incapacity to consent statute, ORS 163.315. [...] Although the legislative commentary is not binding on us, there is no reason to assume from the legislature's probable intent with respect to the consent statute that it intended to adopt a different method for determining when a person is under the age of 16 for the sodomy statute." State v. Hansen, 728 P.2d 538 (1986)

Pennsylvania: Birthday rule

Case law
  • The superior court found that, for the purpose of being able to legally purchase alcohol, one does not turn 21 until the 21st birthday. "In the present case, we are mindful that it is common knowledge and common practice that an individual may not legally be served alcohol, or purchase or consume alcohol, until the day of his twenty-first birthday. When an individual is 'carded' at a liquor store or tavern, it is common knowledge that alcohol will not be served to him or sold to him unless he has proof that it is the twenty-first anniversary of his birth, his twenty-first birthday, or after. It is axiomatic that legislative intent is the polestar of statutory construction. In drafting the criminal statutes at issue in the case at bar, we are convinced that the Legislature was cognizant of this commonly understood and practiced rule for determining the legal age for the purchase and consumption of alcohol. Pursuant to 1 Pa. C.S.A. § 1921, we are bound to presume that the General Assembly did not 'intend a result that is absurd, impossible of execution or unreasonable.' [...] Our Legislature did not intend 18 Pa. C.S.A. § 6308 to be interpreted in a manner which ignores, and indeed contravenes, the commonly accepted and practiced method for determining the legal age for the purchase and consumption of alcohol." Herr v. Booten, 398 Pa. Superior Ct. 166 (1990)
  • The state supreme court ruled that the defendant, who committed an offense a day before his 18th birthday, should be considered a juvenile, but explicitly limited their decision to the Juvenile Act. "It is manifestly clear to us that in common usage a person 'is under' a certain age until the anniversary date of the person's birthdate. In enacting the Juvenile Act, we can fairly assume that the General Assembly was fully cognizant of this common conception. Moreover, since the Juvenile Act is rehabilitative in nature, an extension rather than a restriction of the protective period of the Act is consistent with the directive that all but certain classes of statutes 'shall be liberally construed to effect their objects and to promote justice.' [...] Finally, our decision today is limited to a determination of age under our Juvenile Act." Com. v. Iafrate, 527 Pa. 497 (1991)

Rhode Island: Common law rule

Case law
  • Multiple state supreme court confirmations that "a person reaches his or her next year in age at the first moment of the day prior to the anniversary date of his or her birth", most recently State v. Odiah, No. 2022-296-C.A. (2024)

Tennessee: Mixed

Case law
  • The state supreme court held that, "as an abstract legal proposition", "legally one attains any given age one day before his birthday." However, in examining legislative intent, due to the mixed use of "age" and "birthday" throughout the statue, it found that "it is evident that the Legislature had in mind birthdays and ages in the conventional, usual and ordinary sense of these words." State v. Alley, 594 S.W.2d 381 (1980)

Texas: Birthday rule

Statutory law

Virginia: Common law rule

Opinion of the Attorney General

This will acknowledge receipt of your letter of March 19, 1963, in which you present the question as to whether or not a person whose twenty-first birthday will be celebrated on November 6, 1963, is eligible to register and vote in the general election to be held on November 5, 1963. [...]

In an opinion dated March 25, 1952, published in Report of the Attorney General (1951-1952), p. 126, this office ruled that a child whose sixth birthday is celebrated on October first has reached his sixth birthday on September thirtieth. In that opinion, the Attorney General at that time stated, "I have previously been called upon to study this problem in connection with the age requirements for voting. At that time I discovered that the rule at common law was that a person attains his next year of age on the day prior to his birthday."

It has been consistently held by the courts that the law does not recognize a fraction of a day. A person who will celebrate his twenty-first birthday on the sixth day of November will be commencing his twenty-second year on that date, and attain the age of twenty-one on the previous day.

In my opinion, your question must be answered in the affirmative.

[1962-1963 Op. Atty Gen. Va. 87]

Wisconsin: Birthday rule

Voter registration system / Case law
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  • +1 Excellent answer. Especially for recognizing that the rule is not uniform and providing numerous examples of different circumstances when different rules are applied.
    – ohwilleke
    Mar 7 at 18:52
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It is logically simple why you turn the legal age the day before your birthday. If you were born in January 1, 2000 (like the example above), on December 31, 2020 you have been 'alive' for exactly 21 full years. (the year 2000 plus 20 more years). I have a unique reason I know this to be true. I was born on November 9th, 1998. The day before in 2016 (November 8th) happened to be the 2016 Federal elections in the US. I thought I had missed it by ONE day of being able to vote, but my brother is an attorney and did some enquires and found out that I was legally 18 (in California) the day before my birthday. So I got to vote!!! (NOT happy with the results btw, lol).

Finally this applies for US Federal candidates as well. Congress is sworn in on January 3rd, so a person must be 25 (for the House of Representatives) or 30 (for the Senate) to be sworn in. Thus a person born on January 4th 1996 is eligible to run for the US House in the 2020 elections, as they would be legally assumed to be 25 on January 3, 2021 (the day they are sworn in and the day they are legally 25). The US president is sworn in on January 20th and must be 35 years old, so a person a person born on January 21, 1986 could actually run in the 2020 race, as they would be legally 35 years old on January 20, 2021.

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    I still don't understand the logic. If you were born at, let's say, 3:15 am on on January 1, 2000, then the instant at which you have been alive 21 years is 3:15 am on January 1, 2021 (ignoring leap years and time zones). At no time on December 31, 2020, have you been alive for 21 years. May 25, 2019 at 17:36
  • US Senator en.wikipedia.org/wiki/Rush_Holt_Sr. was nominated, ran and was elected while 29 years old. He was not allowed to sit in the Senate until his 30th birthday, in June...
    – DJohnM
    May 25, 2019 at 18:22
  • @NateEldredge when the common law rule was developed, it was neither customary not possible to measure time that precisely. I agree however that it is illogical. Still, logical or not, it is the way of calculating age that prevails in many jurisdictions.
    – phoog
    May 26, 2019 at 7:41
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    @NateEldredge the law takes the view that "a day begun is a day done". If you have been alive at any moment of the day then as far as the law is concerned you have been alive for the entire day as the law operates in units of one day.
    – A. K.
    May 27, 2019 at 17:05
  • @A.K.: Aha, that makes more sense. So in the above example, as of any moment on December 31, 2020, there are 365*21 days on which you have been alive for at least one moment (again ignoring leap years). This includes two days on which you weren't alive for the entire day: January 1, 2000 (because you were born partway through the day) and December 31, 2020 (because the day is not yet finished) - but they are counted anyway. May 27, 2019 at 17:28
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what is the exact time that person legally turns 18? Is it the midnight before January 1st 2018,

In Germany it would be the midnight (2017-12-31 24:00:00) before January 1st 2018, since the calculation starts at beginning of the day of birth until a full 18 years have passed.


Basicly the Birthday rule cited in @Miles answer is used in Germany for statutes, court orders and legal transactions.

This is defind in Division 4 of the German Civil Code in sections 187-193.

The terminology often used elsewhere tries to express that full years are assumed.

  • Nach Vollendung des 18. Lebensjahres feiert man seinen 18. Geburtstag.
    • After the completion of the 18th year of life you celebrate your 18th birthday.

Also the 24 hour notation is often used to make it clear when a period starts and ends

  • 2023-12-31 24:00:00: moment when the day/month/year ends
  • 2024-01-01 00:00:00: moment when the day/month/year starts
    • the moment of both ('24:00' and '00:00') are the same

For age calculation (meantioned explicitly in §187(2)) the beginning of the day of birth is used.

For someone who was born at 2024-02-29 11:11:11

  • 2024-02-29 00:00:00 will be taken as the beginng of the first year
    • §187(2)
  • 2025-02-28 24:00:00 the first full year has been compleated
    • §188(2) where §187(2) is referenced
  • 2025-03-01 00:00:00 the person is now 1 (full) year old
    • again, the moment of both ('24:00' and '00:00') are the same

The same rule is used for documents such as a passport that is valid for ten years (§5 PassG)

  • Date of issue: 2022-09-21 [00:00:00]
  • Date of expiry: 2032-09-20 [24:00:00]

§191 does not apply in such cases, since the periods are consecutive.


§187 - Beginning of a period of time
...
(2) If the beginning of a day is the determining point in time for the commencement of a period, then this day is included in the calculation of the period. The same applies to the date of birth in computing the age of a person.

§188 - End of a period of time
...
(2) A period of time specified by weeks, by months or by a duration of time comprising more than one month - year, half-year, quarter - ends, in the case governed by section 187 (1), ... or in the case governed by section 187 (2), on the expiry of the day of the last week or of the last month that precedes the day which corresponds in designation or number to the first day of the period of time.

§189 - Calculation of individual periods of time
(1) A half-year is understood to mean a period of six months, a quarter is understood to mean a period of three months, and half a month is understood to mean a period of 15 days.
(2) If a period of time is specified as one or more than one whole month and a half-month, then the 15 days are to be counted last of all.

§191 - Calculation of periods of time If a period of time is determined by months or by years with the meaning that they are not required to run consecutively, then a month is counted as 30 days and a year as 365 days.

§192 - Beginning, middle and end of a month
The beginning of the month is understood to be the first day, the middle of the month the fifteenth day, and the end of month the last day.


Sources:

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