Ruby code to get the date of next Monday (or any day of the week)

For anyone like me who came here looking for a solution in Rails to this problem, as of Rails 5.2 there is a much easier method to do this.

For anyone (like the original poster) not specifically using Rails, this functionality is available in the ActiveSupport gem.

To find the next occurring day of a week, we can simply write something like Date.today.next_occurring(:friday).

See the documentation for more details.

I know this is an old post, but I came up with a couple of methods to quickly get the previous and next day of the week.

# date is a Date object and day_of_week is 0 to 6 for Sunday to Saturday

require 'Date'

def get_next_day(date, day_of_week)
  date + ((day_of_week - date.wday) % 7)
end

def get_previous_day(date, day_of_week)
  date - ((date.wday - day_of_week) % 7)
end

puts today = Date.today
# 2015-02-24

puts next_friday = get_next_day(today, 5)
# 2015-02-27

puts last_friday = get_previous_day(today, 5)
# 2015-02-20

require 'date'

def date_of_next(day)
  date  = Date.parse(day)
  delta = date > Date.today ? 0 : 7
  date + delta
end

Date.today
#=>#<Date: 2011-10-28 (4911725/2,0,2299161)>
date_of_next "Monday"
#=>#<Date: 2011-10-31 (4911731/2,0,2299161)>
date_of_next "Sunday"
#=>#<Date: 2011-10-30 (4911729/2,0,2299161)>