I was looking at the legal age when a person can have a permit. In some states, it is 14 and a half, in others, it is 15 and a half, and so on.

My question is: if someone is born on August 31st and lives in California (where the relevant age is "15 years and 6 months"), will that person be able to get the permit on Feb 28 or March 01 or March 03?

If the answer is March 03 for a person born on August 31st, then what about a person that is born on September 01.

  • 7
    Bonus question for leap years: what if the kid was born on August 29, 30, or 31 of 2008? Mar 4 at 2:28
  • 6
    The language of the statute is "15 years and 6 months", and "month" is defined as a calendar month. But that doesn't quite resolve how the last day is handled. Mar 4 at 2:29
  • 11
    Doesn't matter, DMV will be booked till mid-May /s
    – user71659
    Mar 4 at 2:41
  • Comments have been moved to chat; please do not continue the discussion here. Before posting a comment below this one, please review the purposes of comments. Comments that do not request clarification or suggest improvements usually belong as an answer, on Law Meta, or in Law Chat. Comments continuing discussion may be removed.
    – feetwet
    Mar 4 at 19:50
  • 1
    This is not the kind of thing for which there could be a rule that applies to states in the U.S.A. in general. It can be different in different states. Mar 5 at 14:04

2 Answers 2


They can get the permit on March 1

First, note that there are two different rules that exist for when someone turns a certain age:

  • The "common law rule", which holds that an age is reached at the start of the day before one's corresponding birthday (so someone born August 31, 2000 would turn 15 on August 30, 2015). This rule originates in 17th-century English judicial rulings.
  • The "birthday rule", which holds that an age is reached at the start of the day on the anniversary of one's birth (i.e. on one's birthday). I believe that this is how the vast majority of people in America today think about ages.

Which of these rules is in effect is often left unspecified by statute and is left to the courts to decide, like in the 2014 Michigan Supreme Court case People v Woolfolk. And the same jurisdiction may use different rules in different contexts: for example, at the US federal level, for the calculation of social security eligibility, the SSA uses the common law rule, but for criminal sentencing purposes the birthday rule is used—someone is considered a juvenile until their 18th birthday. Sometimes laws will use phrasing like "a person who has reached their 13th birthday" or "who has not yet attained their 21st birthday" instead of "a person of age 13 or older" or "under the age of 21", thereby skirting the issue.

The California Supreme Court has ruled that the California legislature intended to adopt the birthday rule for the calculation of ages.

While the California Vehicle code does not explicitly define "month", other parts of the California code (1, 2) consistently define it as "a period commencing on any day of a calendar month and extending through the day preceding the corresponding day of the succeeding calendar month, if there is any corresponding day, and if not, through the last day of the succeeding calendar month."

A person is 15 and 6 months of age when 6 months have elapsed since their 15th birthday; the six month period would extend through the final day of February (the 28th or 29th), so they would turn 15 and 6 months on March 1.

then what about a person that is born on September 01

They can get the permit on the same day, March 1.

Further Reading

  • So people born on August (28?), 29, 30, 31, and March 1 all turn "X and a half" on March 1. Fun with edge-case definitions :)
    – Frodyne
    Mar 5 at 8:13

1 March

Under the Acts Interpretation Act, a year is 12 calendar months, so half a year is six calendar months.

calendar month means a period commencing at the beginning of a day of one of the 12 named months and ending—

(a) immediately before the beginning of the corresponding day of the next named month, or

(b) if there is no such corresponding day, at the end of the next named month.

  • 1
    Thanks , your answer is correct too, but I am marking "miles" answer as accepted as "miles" seems new user. Both answers are approximately same.
    – puzzled
    Mar 6 at 1:43

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