diff --git a/services/ical/model/eventModel.go b/services/ical/model/eventModel.go
index 2d92a0d..511ad22 100644
--- a/services/ical/model/eventModel.go
+++ b/services/ical/model/eventModel.go
@@ -37,6 +37,14 @@ func (events Events) Sort() {
 	})
 }
 
+func (events Events) String() string {
+	var str strings.Builder
+	for _, event := range events {
+		str.WriteString(event.String())
+	}
+	return str.String()
+}
+
 type AnonymizedEventDTO struct {
 	Day   string   `db:"Day" json:"day"`
 	Week  string   `db:"Week" json:"week"`
@@ -109,3 +117,7 @@ func (e *Event) GetName() string {
 func (e *Event) SetName(name string) {
 	e.Name = name
 }
+
+func (e *Event) String() string {
+	return e.UUID + e.Day + e.Week + e.Start.String() + e.End.String() + e.Name + e.EventType + e.Compulsory + e.Prof + e.Rooms + e.Notes + e.BookedAt + e.Course + e.Semester
+}
diff --git a/services/ical/model/icalModel.go b/services/ical/model/icalModel.go
index 14121fd..e5cab49 100644
--- a/services/ical/model/icalModel.go
+++ b/services/ical/model/icalModel.go
@@ -92,3 +92,7 @@ func ToJSONTime(timeString string) JSONTime {
 	}
 	return JSONTime(t)
 }
+
+func (j JSONTime) String() string {
+	return time.Time(j).Format(DefaultDateLayout)
+}
diff --git a/services/ical/service/ical/ical.go b/services/ical/service/ical/ical.go
index ba8e7f2..11759e0 100644
--- a/services/ical/service/ical/ical.go
+++ b/services/ical/service/ical/ical.go
@@ -23,6 +23,7 @@ import (
 	"htwkalender/ical/model"
 	"htwkalender/ical/service/connector"
 	htwkalenderGrpc "htwkalender/ical/service/connector/grpc"
+	"htwkalender/ical/service/functions"
 	"log/slog"
 	"time"
 )
@@ -31,7 +32,7 @@ const expirationTime = 5 * time.Minute
 
 var FeedDeletedError = fmt.Errorf("feed deleted")
 
-func Feed(app model.AppType, token string) (string, error) {
+func Feed(app model.AppType, token string) (string, string, error) {
 
 	var events model.Events
 	modules := map[string]model.FeedCollection{}
@@ -47,17 +48,17 @@ func Feed(app model.AppType, token string) (string, error) {
 		// get feed by token
 		feed, err := htwkalenderGrpc.GetFeed(token, app.GrpcClient)
 		if err != nil {
-			return "", err
+			return "", "", err
 		}
 
 		if feed.Deleted {
-			return "", FeedDeletedError
+			return "", "", FeedDeletedError
 		}
 
 		// Get all events for modules
 		events, err = htwkalenderGrpc.GetEvents(feed.Modules, app.GrpcClient)
 		if err != nil {
-			return "", err
+			return "", "", err
 		}
 
 		// Sort events by start date
@@ -68,11 +69,14 @@ func Feed(app model.AppType, token string) (string, error) {
 		}
 	}
 
+	// Generate one Hash for E-TAG from all events and modules
+	etag := functions.HashString(events.String() + fmt.Sprint(modules))
+
 	b := bytes.Buffer{}
 	goics.NewICalEncode(&b).Encode(IcalModel{Events: events, Mapping: modules})
 	icalFeed := &model.FeedModel{Content: b.String(), ExpiresAt: model.JSONTime(time.Now().Add(expirationTime))}
 
-	return icalFeed.Content, nil
+	return icalFeed.Content, etag, nil
 }
 
 func FeedRecord(app model.AppType, token string) (model.FeedRecord, error) {
diff --git a/services/ical/service/routes.go b/services/ical/service/routes.go
index c92a0f7..99117fe 100644
--- a/services/ical/service/routes.go
+++ b/services/ical/service/routes.go
@@ -34,7 +34,7 @@ func AddFeedRoutes(app model.AppType) {
 	app.Fiber.Get("/api/feed", func(c fiber.Ctx) error {
 
 		token := c.Query("token")
-		results, err := ical.Feed(app, token)
+		results, eTag, err := ical.Feed(app, token)
 
 		if errors.Is(err, ical.FeedDeletedError) {
 			return c.SendStatus(fiber.StatusGone)
@@ -48,6 +48,7 @@ func AddFeedRoutes(app model.AppType) {
 		c.Response().Header.Set("charset", "utf-8")
 		c.Response().Header.Set("Content-Disposition", "inline")
 		c.Response().Header.Set("filename", "calendar.ics")
+		c.Response().Header.Set("ETag", eTag)
 
 		return c.SendString(results)
 	})