diff --git a/docs/onebusaway-gtfs-transformer-cli.md b/docs/onebusaway-gtfs-transformer-cli.md
index 92873436..ec386d41 100644
--- a/docs/onebusaway-gtfs-transformer-cli.md
+++ b/docs/onebusaway-gtfs-transformer-cli.md
@@ -343,13 +343,13 @@ those manually.
 
 #### Remove Old Calendar Statements
 
-RemoveOldCalendarStatements is an operation designed to remove calendar entries that are no longer valid on today's date.
+RemoveOldCalendarStatements is an operation designed to remove calendar and calendar dates entries that are no longer valid on today's date.
 
-By default, it deletes entries from the calendar.txt file whose end_date field has passed.
+By default, it deletes entries from both the calendar.txt and calendar_dates.txt files, where the end_date in calendar.txt or the date field in calendar_dates.txt has passed.
 
-With the remove_today attribute added to the JSON transformer snippet, users can control whether calendar entries valid for today are included or excluded in the output GTFS.
+With the remove_today attribute added to the JSON transformer snippet, users can control whether entries in calendar or calendar_dates that are valid for today are included or excluded in the GTFS output.
 
-  * If remove_today is set to true, the transformer will remove the calendar entries for the current date.
+  * If remove_today is set to true, the transformer will remove entries for the current date.
   
 ```
   {"op":"transform", "class":"org.onebusaway.gtfs_transformer.impl.RemoveOldCalendarStatements", "remove_today":true}
@@ -361,6 +361,15 @@ With the remove_today attribute added to the JSON transformer snippet, users can
 {"op":"transform", "class":"org.onebusaway.gtfs_transformer.impl.RemoveOldCalendarStatements", "remove_today":false}
 ```
 
+Additionally, after truncating the calendar entries, it is recommended to use a **retain operation** to ensure that only trips with valid calendar dates are retained. 
+
+Without this retain operation, the `trips.txt` file will contain trips with non-existent calendar dates, leading to invalid data.
+
+```
+{"op":"transform", "class":"org.onebusaway.gtfs_transformer.impl.RemoveOldCalendarStatements", "remove_today":false}
+{"op":"retain", "match":{"file":"calendar_dates.txt"}, "retainBlocks":false}
+```
+
 #### Deduplicate Calendar Entries
 
 Finds GTFS service_ids that have the exact same set of active days and consolidates each set of duplicated
diff --git a/onebusaway-gtfs-transformer/src/main/java/org/onebusaway/gtfs_transformer/impl/RemoveOldCalendarStatements.java b/onebusaway-gtfs-transformer/src/main/java/org/onebusaway/gtfs_transformer/impl/RemoveOldCalendarStatements.java
index 5fa49183..38f369b6 100644
--- a/onebusaway-gtfs-transformer/src/main/java/org/onebusaway/gtfs_transformer/impl/RemoveOldCalendarStatements.java
+++ b/onebusaway-gtfs-transformer/src/main/java/org/onebusaway/gtfs_transformer/impl/RemoveOldCalendarStatements.java
@@ -20,6 +20,7 @@
 
 import org.onebusaway.csv_entities.schema.annotations.CsvField;
 import org.onebusaway.gtfs.model.ServiceCalendar;
+import org.onebusaway.gtfs.model.ServiceCalendarDate;
 import org.onebusaway.gtfs.services.GtfsMutableRelationalDao;
 import org.onebusaway.gtfs_transformer.services.GtfsTransformStrategy;
 import org.onebusaway.gtfs_transformer.services.TransformContext;
@@ -64,5 +65,16 @@ public void run(TransformContext transformContext, GtfsMutableRelationalDao gtfs
         for (ServiceCalendar serviceCalendar : serviceCalendarsToRemove) {
             removeEntityLibrary.removeCalendar(gtfsMutableRelationalDao, serviceCalendar.getServiceId());
         }
+
+        Set<ServiceCalendarDate> serviceCalendarDatesToRemove = new HashSet<ServiceCalendarDate>();
+        for (ServiceCalendarDate calendarDate : gtfsMutableRelationalDao.getAllCalendarDates()) {
+            if (calendarDate.getDate().getAsDate().before(today)) {
+                serviceCalendarDatesToRemove.add(calendarDate);
+            }
+        }
+        for (ServiceCalendarDate serviceCalendarDate : serviceCalendarDatesToRemove) {
+            // here we can't delete the trips as the serviceid may be active elsewhere
+            removeEntityLibrary.removeServiceCalendarDate(gtfsMutableRelationalDao, serviceCalendarDate);
+        }
     }
 }
\ No newline at end of file
diff --git a/onebusaway-gtfs-transformer/src/test/java/org/onebusaway/gtfs_transformer/impl/RemoveOldCalendarStatementsTest.java b/onebusaway-gtfs-transformer/src/test/java/org/onebusaway/gtfs_transformer/impl/RemoveOldCalendarStatementsTest.java
index 3519bfc2..87a2d393 100644
--- a/onebusaway-gtfs-transformer/src/test/java/org/onebusaway/gtfs_transformer/impl/RemoveOldCalendarStatementsTest.java
+++ b/onebusaway-gtfs-transformer/src/test/java/org/onebusaway/gtfs_transformer/impl/RemoveOldCalendarStatementsTest.java
@@ -31,11 +31,18 @@ public void setup() throws IOException{
         String startDate = getCurrentDateFormatted(-3);
         String endDate = getCurrentDateFormatted(null);
 
+        // Define additional date for testing purposes, relative to startDate
+        String threeDaysFromStartDate = getCurrentDateFormatted(3);
+
         _gtfs.putCalendars(
             1,
             "start_date="+startDate,
             "end_date="+endDate
         );
+
+        // Insert calendar dates entries
+        _gtfs.putCalendarDates("sid0="+startDate+","+endDate+","+
+            threeDaysFromStartDate);
     }
 
     @Test
@@ -46,6 +53,8 @@ public void testRemoveCalendarForToday() throws IOException  {
         removeOldCalendarStatements.run(_context, dao);
         // Verify that GtfsMutableRelationalDao object no longer contains any calendar entries after removing the calendar for today's date
         assertEquals(0,dao.getAllCalendars().size());
+        // Verify that GtfsMutableRelationalDao object no longer contains any calendar dates entries after removing invalid dates, including today's date
+        assertEquals(0,dao.getAllCalendarDates().size());
     }
 
     @Test
@@ -55,6 +64,8 @@ public void testRemoveCalendar() throws IOException  {
         removeOldCalendarStatements.run(_context, dao);
         // Verify that GtfsMutableRelationalDao object still contain the initially added calendar entry
         assertEquals(1,dao.getAllCalendars().size());
+        // Verify that GtfsMutableRelationalDao object contains two calendar dates entries after removing invalid dates
+        assertEquals(2,dao.getAllCalendarDates().size());
     }
 
     // Helper function to get today's date in the required format