A couple methods to prorate prices by calculating the remaining days of the month

prorating_prices.rb

require 'date'

def days_remaining_in_month
  day_of_month = Time.now.day
  (days_in_month(Time.now.year, Time.now.month) - day_of_month)
end

def prorated_price_today(price)
  day_of_month = Time.now.day
  percent_of_month_remaining = BigDecimal(days_remaining_in_month.to_s) / BigDecimal(days_in_month(Time.now.year, Time.now.month).to_s)
  (BigDecimal(price.to_s) * BigDecimal(percent_of_month_remaining.to_s)).round(2)
end

def days_in_month(year, month)
  (Date.new(year, 12, 31) << (12-month)).day
end