Question

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How to calculate how many years passed since a given date in Ruby?

I am trying to convert a datestamp taken from the database into value indicating how many years old a person is. I am sure this easy, but I can’t seem to figure it out.

Answer 1

Assuming the datestamp is being retrieved as a DateTime value:

require 'date'

birth_date = DateTime.parse('1970-01-01 1:35 AM')
time_now = DateTime.now

(time_now - birth_date).to_i / 365 # => 41
(time_now - birth_date).to_f / 365 # => 41.38907504054664

birth_date is a mock value for what you should be retrieving from your database. The first value is years, the second is fractional years.

Alternately, you can do it this way:

years = time_now.year - birth_date.year
years -= 1 if (birth_date.month > time_now.month)
years # => 41

This adjusts in case the person hasn’t had their birthday yet. For instance, tweaking the birthday:

birth_date = DateTime.parse('1970-12-31 11:59 PM')
years = time_now.year - birth_date.year
years -= 1 if (birth_date.month > time_now.month)
years # => 40