Given a date, this class is used to find the next payday being the 1st or the 15th. If the payday falls on a weekend or holiday the payday is adjusted to the business day. Note that you'll need to install the gems 'holidays' and 'active_support'. Not sure if this last on if available outside of rails

payday.rb

require 'date'
require 'active_support/core_ext/integer/inflections' # Used for printing date as human text
require 'holidays' # Gives access to holiays

class Payday
  def initialize(query_date)
    @query_date = query_date
    @next_payday = 'unknown'
  end

  # Gets next business day payday
  def get_next_payday
    self.set_next_standard_payday
    self.holiday_adjustment
    self.weekend_adjustment
    
    "Payday will be " + @next_payday.strftime("%a %b #{@next_payday.day.ordinalize}")
  end

  # Gives us the next payday for of either the 1st or 15th of the month
  def set_next_standard_payday
    day, month, year = self.set_date_components

    if day == 1
      @next_payday = @query_date
    elsif day.between?(2, 15)
      @next_payday = Date.new(year, month, 15)
    elsif day.between?(16, 31)
      month == 12 ? @next_payday = Date.new(year + 1, 1, 1) : @next_payday = Date.new(year, month + 1, 1)
    end
  end

  # Sets the day, month and year from @query_date
  def set_date_components
    return @query_date.day, @query_date.month, @query_date.year
  end

  # Adjust payday if it falls on a holiday
  def holiday_adjustment
    #checks to see if @next_payday is a US holday
    if @next_payday.holidays(:us).any?
      @next_payday = @next_payday - 1
    end
  end

  # Adjust payday if it falls on a weekend
  def weekend_adjustment
    if @next_payday.saturday?
      @next_payday = @next_payday - 1
    elsif @next_payday.sunday?
      @next_payday = @next_payday - 2
    end
  end
end

Here is the output from running in IRB

irb(main):054:0* date = Date.new(2014, 04, 01) => #<Date: 2014-04-01 ((2456749j,0s,0n),+0s,2299161j)> irb(main):055:0> payday = Payday.new(date) => #<Payday:0x007fe0b5c88fa0 @query_date=#<Date: 2014-04-01 ((2456749j,0s,0n),+0s,2299161j)>, @next_payday="unknown"> irb(main):056:0> payday.get_next_payday => "Payday will be Tue Apr 1st" irb(main):057:0> irb(main):058:0* date = Date.new(2014, 06, 14) => #<Date: 2014-06-14 ((2456823j,0s,0n),+0s,2299161j)> irb(main):059:0> payday = Payday.new(date) => #<Payday:0x007fe0b5c6bf90 @query_date=#<Date: 2014-06-14 ((2456823j,0s,0n),+0s,2299161j)>, @next_payday="unknown"> irb(main):060:0> payday.get_next_payday => "Payday will be Fri Jun 13th" irb(main):061:0> irb(main):062:0* date = Date.new(2014, 12, 30) => #<Date: 2014-12-30 ((2457022j,0s,0n),+0s,2299161j)> irb(main):063:0> payday = Payday.new(date) => #<Payday:0x007fe0b5c50628 @query_date=#<Date: 2014-12-30 ((2457022j,0s,0n),+0s,2299161j)>, @next_payday="unknown"> irb(main):064:0> payday.get_next_payday => "Payday will be Wed Dec 31st" irb(main):065:0> irb(main):066:0* date = Date.new(2005, 12, 30) => #<Date: 2005-12-30 ((2453735j,0s,0n),+0s,2299161j)> irb(main):067:0> payday = Payday.new(date) => #<Payday:0x007fe0b5c30c38 @query_date=#<Date: 2005-12-30 ((2453735j,0s,0n),+0s,2299161j)>, @next_payday="unknown"> irb(main):068:0> payday.get_next_payday => "Payday will be Fri Dec 30th" irb(main):069:0>