diff --git a/app/src/app.js b/app/src/app.js
index 3a88822..ca5bf39 100644
--- a/app/src/app.js
+++ b/app/src/app.js
@@ -52,7 +52,8 @@ const {
   getUsernameToIdMap,
   getUsersInfo,
   confirmationMessage,
-  formatAttachmentsForStatusMessage
+  formatAttachmentsForStatusMessage,
+  membersHaveScheduleConflict
 } = require('./helpers')(
   fetch,
   url,
@@ -217,9 +218,10 @@ async function executeCommand({ team_id, user_id, command, token }) {
   // TODO: a new state out of the reducer should already include the team_id
   nextState.team_id = team_id;
 
-  await saveState(nextState);
   switch (action.type) {
     case 'SCHEDULE':
+      const allEvents = getEventsFor({ team_id })
+      membersHaveScheduleConflict(allEvents, action)
       scheduler.add([nextState]);
       break;
     case 'HALT':
@@ -231,6 +233,7 @@ async function executeCommand({ team_id, user_id, command, token }) {
       scheduler.reschedule([nextState]);
       break;
   }
+  await saveState(nextState);
 
   return {
     action,
diff --git a/app/src/helpers.js b/app/src/helpers.js
index 2d499b6..7c81e77 100644
--- a/app/src/helpers.js
+++ b/app/src/helpers.js
@@ -279,6 +279,38 @@ module.exports = (
       }))
     }])
   }
+  
+function membersHaveScheduleConflict(events, { userInfos, time, frequency}, standupTimeInMinutes = 15) {
+  let weekends = new Set(["SATERDAYS", "SUNDAYS", "WEEKENDS"])
+  let weekdays = new Set(["MONDAYS", "TUESDAYS", "WEDNESDAYS", "THURSDAYS", "FRIDAYS"])
+  
+  const membersOfNextEvent = new Set(userInfos.map((user) => user.user_id))
+  let timeOfNextEvent = (time.hh * 100) + time.mm;
+  events.forEach(event => {
+      let timeOfScheduledEvent = (event.time.hh * 100) + event.time.mm;
+      event.members.forEach(member => {
+          if (Math.abs(timeOfScheduledEvent - timeOfNextEvent) <= standupTimeInMinutes) {
+              if (membersOfNextEvent.has(member.user_id)) {
+                  if (frequency === event.frequency) {
+                      throw new customError('schedule conflict', EH1000)
+                  }
+                  switch (event.frequency) {
+                      case 'EVERYDAY':
+                          throw new customError('schedule conflict', EH1000)
+                      case 'WEEKENDS':
+                          if (weekends.has(frequency)) {
+                              throw new customError('schedule conflict', EH1000)
+                          }
+                      case 'WEEKDAYS':
+                          if (weekdays.has(frequency)) {
+                              throw new customError('schedule conflict', EH1000)
+                          }
+                  }
+              }
+          }
+      })
+  })
+}
 
   return {
     notifyUsers,
@@ -287,6 +319,7 @@ module.exports = (
     getUsernameToIdMap,
     getSecretsAndSave,
     confirmationMessage,
-    formatAttachmentsForStatusMessage
+    formatAttachmentsForStatusMessage,
+    membersHaveScheduleConflict
   };
 };
\ No newline at end of file