Get Person'S Age in Ruby

Get person's age in Ruby

I know I'm late to the party here, but the accepted answer will break horribly when trying to work out the age of someone born on the 29th February on a leap year. This is because the call to birthday.to_date.change(:year => now.year) creates an invalid date.

I used the following code instead:

require 'date'

def age(dob)
now =
now.year - dob.year - ((now.month > dob.month || (now.month == dob.month && >= ? 0 : 1)

How to display ages instead of dates of birth, in Ruby on Rails?

Rails has a couple of Date-Helpers, among them distance_of_time_in_words:

As far as I remember it adds an "about x years", so it might be not useful in your particular situation unless you take a look at the source and adapt it.

Otherwise you can calculate with years directly calling (or dob.year).

Age calculation in Ruby

For the validator, you can use a custom method:

validate :over_18

def over_18
if dob + 18.years >=
errors.add(:dob, "can't be under 18")

Ruby age method using date of birth including months

While this may be better posted to a codereview site, I will still give you my thoughts.

You have written a fairly long method for what could be a couple smaller ones.

First, I would write one method that takes the number of years an months and separate that into its own function.

def readable_age(years, months)
# for under 1 year olds
if years == 0
return months > 1 ? months.to_s + " months old" : months.to_s + " month old"

# for 1 year olds
elsif years == 1
return months > 1 ? years.to_s + " year and " + months.to_s + " months old" : years.to_s + " year and " + months.to_s + " month old"

# for older than 1
return months > 1 ? years.to_s + " years and " + months.to_s + " months old" : years.to_s + " years and " + months.to_s + " month old"

Though, if you do not mind adding some dependencies to your project, you can take advantage of the actionview gem, you can take advantage of the pluralize function. Something along the lines of

def readable_age(years, months)
year_text = ''
if years != 0
year_text = "#{years} #{pluralize('year', years)} and "

"#{year_text}#{pluralize('month', months)} old"

Now for your function to calculate the number of years and months.

def age(t)
dob = self.date_of_birth

months = (t.year * 12 + t.month) - (dob.year * 12 + dob.month)

# months / 12 will give the number of years
# months % 12 will give the number of months
readable_age(months / 12, months % 12)


The reason I am passing a date object into the age function is to allow you to calculate the the age of a person for a given time stamp. It also makes it easier to test a function if it produces the same result given the same inputs.

Find the name and age of the oldest person in a txt file using ruby

"figure out who the oldest person/people are on this list", so multiple results are possible. Ruby has a group_by method, which groups an enumerable by a common property. What property? The property you specify in the block.

grouped ='nameage.txt') do |f|
f.group_by do |line|
line.split(":").last.to_i # using OP's line

p grouped # just to see what it looks like
puts grouped.max.last # end result

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