Calculate age in Rails with a birthday

January 28th, 2008

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This is one of those random things that shows up every now and then.

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#this will approximate the user's age
  def calculate_age(birthday)
    Date.today.year - birthday.to_date.year
  end
 
#this is exact
def calculate_age(birthday)
  (Date.today - birthday).to_i / 365
end
Posted by Jonathan Filed in Ruby on Rails

11 Responses to “Calculate age in Rails with a birthday”

  1. anonymousNo Gravatar Says:
    February 25th, 2008 at 3:27 pm

    the result of the second example is not very accurate because leap years are ignored.
    to get around this, just use the following:

    def age
  now = Time.now.utc
  now.year - birthday.year - (birthday.to_time.change(:year => now.year) > now ? 1 : 0)
end
  2. JonathanNo Gravatar Says:
    February 25th, 2008 at 7:32 pm
    Thanks for that post. When we did the age calculation it was meant to give us an approximation of our user base. Since it was not critical to have 100% accurate information, leap year was overlooked :)
  3. anonymousNo Gravatar Says:
    February 28th, 2008 at 9:33 pm

    i also was not aware of all the gotchas involved with dates, times and timezones…

    somehow i missed this detail:
    you cannot compare DateTime with Time, so use the to_date Method on both Objects

    def age
      now = Time.now.utc.to_date
      now.year - birthday.year - (birthday.to_date.change(:year => now.year) > now ? 1 : 0)
    end

  4. TobiNo Gravatar Says:
    March 13th, 2008 at 6:32 am

    Hey thanks for your solution.

    The exact age with leap years seams a bit tricky. Unfortunately the above solution has still 2 problems:
    1. it changes the actual birthday data which we may need later in progress
    2. it raises an “InvalidDate Exception” if now is a leapyear day, e.g. 2008/2/29

    I solved this with:

     def age( birthday )
    return 0 unless info.birthday
    age = Date.today.year - birthday.year
    age -= 1 if birthday > Date.today.years_ago( age )
    age
  end

    check http://pastie.caboo.se/165173 for the belonging tests

  5. TobiNo Gravatar Says:
    March 13th, 2008 at 6:34 am

    ups it should be:

    def age( birthday )
    age = Date.today.year - birthday.year
    age -= 1 if birthday > Date.today.years_ago( age )
    age
end
  6. Naveen DittakaviNo Gravatar Says:
    March 24th, 2008 at 10:41 am

    Hi Tobi,

    We couldn’t get the above to work. Here’s what worked for us in the controller:

    birthday = Time.mktime(params[:year], params[:month].to_i, params[:day].to_i)
@age = age(birthday)

protected

def age( birthday )
age = Date.today.year - birthday.year
today = Time.now
age -= 1 if birthday > today.years_ago( age )
age
end
  7. apiNo Gravatar Says:
    April 11th, 2008 at 6:29 am

    ( (Date.today - birthday).to_i / 365.25).floor this will work with leap-year

  8. rolfNo Gravatar Says:
    April 15th, 2008 at 5:56 am

    I’ve put the next few lines in my application_helper, I’m using it to calculate the age of people today(but this could be any date), just passing @person.birthday to it. gr rolf

      def age(birthday)
    y=(Date.today.year) - (birthday.year)
    m=(Date.today.month)-(birthday.month)
    d=(Date.today.day)-(birthday.day)
        case
           when (m<0)
                      age=y-1     #april-mei=-1; april-april=0; april-maart=1#15-15=0; 15-16=-1; 15-13=2
           when (m=0)
                        case
                            when(d0)
                              age=y
                        end
            when (m>0)
              age=y
         end
    age
  end
  9. rolfNo Gravatar Says:
    April 15th, 2008 at 6:03 am 
    def age(birthday)
    y=(Date.today.year) - (birthday.year)
    m=(Date.today.month)-(birthday.month)
    d=(Date.today.day)-(birthday.day)
        case
           when (m<0)
                      age=y-1
           when (m=0)
                        case
                            when(d0)
                              age=y
                        end
            when (m>0)
              age=y
         end
    age
  end
  10. NOVNo Gravatar Says:
    May 10th, 2008 at 1:56 pm 
    class Date
  def to_age
    integer_style = "%Y%m%d"
    today = Date.today.strftime(integer_style).to_i
    birthday = Date.today.strftime(integer_style).to_i
    (today - birthday) / 10000
  end
end

    => birthday.to_age

    If the birthday.class.class_name == Time, you can use below.

    http://d.hatena.ne.jp/secondlife/20050922/1127376501

  11. NOVNo Gravatar Says:
    May 10th, 2008 at 2:20 pm

    today, birthday = [Date.today, self].map do |d|
    d.strftime(”%Y%m%d”).to_i
    end
    (today - birthday) / 10000

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