diff --git a/21_Calendar/ruby/calendar.rb b/21_Calendar/ruby/calendar.rb
new file mode 100644
index 00000000..4f7061d7
--- /dev/null
+++ b/21_Calendar/ruby/calendar.rb
@@ -0,0 +1,113 @@
+class Calendar
+  def parse_input
+    days_mapping = {
+      "sunday": 0,
+      "monday": -1,
+      "tuesday": -2,
+      "wednesday": -3,
+      "thursday": -4,
+      "friday": -5,
+      "saturday": -6,
+    }
+
+    day = 0
+    leap_day = false
+    correct_day_input = false
+
+    while !correct_day_input 
+      print "INSERT THE STARTING DAY OF THE WEEK OF THE YEAR: "
+      weekday = gets.chomp!
+
+      days_mapping.each do |k, v|
+        if k.to_s == weekday.downcase.to_s
+          day = v
+          correct_day_input = true
+          break
+        end
+      end
+    end
+
+    while true
+      print "IS IT A LEAP YEAR?: "
+      leap = gets.chomp!
+      if "y" == leap.downcase.to_s
+        leap_day = true
+        break
+      end
+
+      if "n" == leap.downcase.to_s
+        leap_day = false
+        break
+      end
+    end
+
+    return day, leap_day
+  end
+
+  def start(weekday, leap_year)
+    months_days = [0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31]
+    days = "S        M        T        W        T        F        S\n"
+    sep = "*" * 59
+    years_day = 365
+    d = weekday
+
+    if leap_year
+      months_days[2] = 29
+      years_day = 366
+    end
+
+    months_names = [
+      " JANUARY ",
+      " FEBRUARY",
+      "  MARCH  ",
+      "  APRIL  ",
+      "   MAY   ",
+      "   JUNE  ",
+      "   JULY  ",
+      "  AUGUST ",
+      "SEPTEMBER",
+      " OCTOBER ",
+      " NOVEMBER",
+      " DECEMBER",
+    ]
+
+    days_count = 0
+
+    for n in (1..12) do
+      days_count += months_days[n - 1]
+      print "** #{days_count} ****************** #{months_names[n - 1]} ****************** #{years_day - days_count} **\n"
+      print days
+      print sep
+      for nnn in (1..6) do
+        print "\n"
+        for g in (1..7) do
+          d += 1
+          d2 = d - days_count
+
+          break if d2 > months_days[n]
+
+          if d2 <= 0
+            print "         "
+          elsif d2 < 10
+            print " #{d2}       "
+          else
+            print "#{d2}       "
+          end
+        end
+
+        print "\n\n"
+
+        break if d2 >= months_days[n]
+      end
+      d -= g if d2 > months_days[n]
+      print "\n"
+    end
+    print "\n"
+  end
+end
+
+if __FILE__ == $0
+  calendar = Calendar.new
+  input = calendar.parse_input
+  calendar.start(input[0], input[1])
+end
\ No newline at end of file