diff --git a/zipline/transforms/utils.py b/zipline/transforms/utils.py
index 0891747f..abf2223a 100644
--- a/zipline/transforms/utils.py
+++ b/zipline/transforms/utils.py
@@ -29,7 +29,7 @@ from numbers import Integral
 import pandas as pd
 
 from zipline.protocol import Event
-from zipline.utils.tradingcalendar import non_trading_days
+from zipline.utils import tradingcalendar
 from zipline.gens.utils import assert_sort_unframe_protocol, hash_args
 
 log = logbook.Logger('Transform')
@@ -209,9 +209,6 @@ class EventWindow(object):
         if self.market_aware:
             assert self.window_length and self.delta is None, \
                 "Market-aware mode only works with full-day windows."
-            self.all_holidays = deque(non_trading_days)
-            self.cur_holidays = deque()
-
         # Non-market-aware mode requires a timedelta.
         else:
             assert self.delta and not self.window_length, \
@@ -244,9 +241,6 @@ class EventWindow(object):
         # adding new ticks.
         self.handle_add(event)
 
-        if self.market_aware:
-            self.add_new_holidays(event.dt)
-
         # Clear out any expired events. drop_condition changes depending
         # on whether or not we are running in market_aware mode.
         #
@@ -262,25 +256,11 @@ class EventWindow(object):
             # behavior for removing ticks.
             self.handle_remove(popped)
 
-    def add_new_holidays(self, newest):
-        # Add to our tracked window any untracked holidays that are
-        # older than our newest event. (newest should always be
-        # self.ticks[-1])
-        while len(self.all_holidays) > 0 and self.all_holidays[0] <= newest:
-            self.cur_holidays.append(self.all_holidays.popleft())
-
-    def drop_old_holidays(self, oldest):
-        # Drop from our tracked window any holidays that are older
-        # than our oldest tracked event. (oldest should always
-        # be self.ticks[0])
-        while len(self.cur_holidays) > 0 and self.cur_holidays[0] < oldest:
-            self.cur_holidays.popleft()
-
     def out_of_market_window(self, oldest, newest):
-        self.drop_old_holidays(oldest)
-        calendar_dates_between = (newest.date() - oldest.date()).days
-        holidays_between = len(self.cur_holidays)
-        trading_days_between = calendar_dates_between - holidays_between
+        oldest_index = tradingcalendar.trading_days.searchsorted(oldest)
+        newest_index = tradingcalendar.trading_days.searchsorted(newest)
+
+        trading_days_between = newest_index - oldest_index
 
         # "Put back" a day if oldest is earlier in its day than newest,
         # reflecting the fact that we haven't yet completed the last
diff --git a/zipline/utils/tradingcalendar.py b/zipline/utils/tradingcalendar.py
index 7de9e621..78dd1bf8 100644
--- a/zipline/utils/tradingcalendar.py
+++ b/zipline/utils/tradingcalendar.py
@@ -14,6 +14,7 @@
 # limitations under the License.
 
 
+import pandas as pd
 import pytz
 
 from datetime import datetime
@@ -176,6 +177,15 @@ def get_non_trading_days(start, end):
     # - President Gerald R. Ford - Jan 2, 2007
     non_trading_days.append(datetime(2007, 1, 2, tzinfo=pytz.utc))
 
-    return sorted(non_trading_days)
+    return pd.DatetimeIndex(sorted(non_trading_days))
 
-non_trading_days = get_non_trading_days(start, end)
+
+def get_trading_days(start, end):
+    business_days = pd.DatetimeIndex(start=start, end=end,
+                                     freq=pd.datetools.BDay())
+
+    non_trading_days = get_non_trading_days(start, end)
+
+    return business_days - non_trading_days
+
+trading_days = get_trading_days(start, end)