diff --git a/src/domain/session/room/timeline/ReactionsViewModel.js b/src/domain/session/room/timeline/ReactionsViewModel.js
index 5f3b01a7..62610ed1 100644
--- a/src/domain/session/room/timeline/ReactionsViewModel.js
+++ b/src/domain/session/room/timeline/ReactionsViewModel.js
@@ -23,23 +23,47 @@ export class ReactionsViewModel {
         this._reactions = this._map.sortValues((a, b) => a._compare(b));
     }
 
-    update(annotations) {
-        for (const key in annotations) {
-            if (annotations.hasOwnProperty(key)) {
-                const annotation = annotations[key];
+    update(annotations, pendingAnnotations) {
+        if (annotations) {
+            for (const key in annotations) {
+                if (annotations.hasOwnProperty(key)) {
+                    const annotation = annotations[key];
+                    const reaction = this._map.get(key);
+                    if (reaction) {
+                        if (reaction._tryUpdate(annotation)) {
+                            this._map.update(key);
+                        }
+                    } else {
+                        this._map.add(key, new ReactionViewModel(key, annotation, 0, this._parentEntry));
+                    }
+                }
+            }
+        }
+        if (pendingAnnotations) {
+            for (const [key, count] of pendingAnnotations.entries()) {
                 const reaction = this._map.get(key);
                 if (reaction) {
-                    if (reaction._tryUpdate(annotation)) {
+                    if (reaction._tryUpdatePending(count)) {
                         this._map.update(key);
                     }
                 } else {
-                    this._map.add(key, new ReactionViewModel(key, annotation, this._parentEntry));
+                    this._map.add(key, new ReactionViewModel(key, null, count, this._parentEntry));
                 }
             }
         }
         for (const existingKey of this._map.keys()) {
-            if (!annotations.hasOwnProperty(existingKey)) {
+            const hasPending = pendingAnnotations?.has(existingKey);
+            const hasRemote = annotations?.hasOwnProperty(existingKey);
+            if (!hasRemote && !hasPending) {
                 this._map.remove(existingKey);
+            } else if (!hasRemote) {
+                if (this._map.get(existingKey)._tryUpdate(null)) {
+                    this._map.update(existingKey);
+                }
+            } else if (!hasPending) {
+                if (this._map.get(existingKey)._tryUpdatePending(0)) {
+                    this._map.update(existingKey);
+                }
             }
         }
     }
@@ -50,43 +74,65 @@ export class ReactionsViewModel {
 }
 
 class ReactionViewModel {
-    constructor(key, annotation, parentEntry) {
+    constructor(key, annotation, pendingCount, parentEntry) {
         this._key = key;
         this._annotation = annotation;
+        this._pendingCount = pendingCount;
         this._parentEntry = parentEntry;
     }
 
     _tryUpdate(annotation) {
-        if (
+        const oneSetAndOtherNot = !!this._annotation !== !!annotation;
+        const bothSet = this._annotation && annotation;
+        const areDifferent = bothSet &&  (
             annotation.me !== this._annotation.me ||
             annotation.count !== this._annotation.count ||
             annotation.firstTimestamp !== this._annotation.firstTimestamp
-        ) {
+        );
+        if (oneSetAndOtherNot || areDifferent) {
             this._annotation = annotation;
             return true;
         }
         return false;
     }
 
+    _tryUpdatePending(pendingCount) {
+        if (pendingCount !== this._pendingCount) {
+            this._pendingCount = pendingCount;
+            return true;
+        }
+        return false;
+    }
+
     get key() {
         return this._key;
     }
 
     get count() {
-        return this._annotation.count;
+        return (this._annotation?.count || 0) + this._pendingCount;
+    }
+
+    get isPending() {
+        return this._pendingCount !== 0;
     }
 
     get haveReacted() {
-        return this._annotation.me;
+        return this._annotation?.me || this.isPending;
     }
 
     _compare(other) {
-        const a = this._annotation;
-        const b = other._annotation;
-        if (a.count !== b.count) {
-            return b.count - a.count;
+        if (this.count !== other.count) {
+            return other.count - this.count;
         } else {
-            return a.firstTimestamp - b.firstTimestamp;
+            const a = this._annotation;
+            const b = other._annotation;
+            if (a && b) {
+                return a.firstTimestamp - b.firstTimestamp;
+            } else if (a) {
+                return -1;
+            } else {
+                return 1;
+            }
         }
     }
 
@@ -97,4 +143,5 @@ class ReactionViewModel {
             return this._parentEntry.react(this.key);
         }
     }
+}
 }
\ No newline at end of file
diff --git a/src/domain/session/room/timeline/tiles/BaseMessageTile.js b/src/domain/session/room/timeline/tiles/BaseMessageTile.js
index 719571a9..db126432 100644
--- a/src/domain/session/room/timeline/tiles/BaseMessageTile.js
+++ b/src/domain/session/room/timeline/tiles/BaseMessageTile.js
@@ -24,7 +24,7 @@ export class BaseMessageTile extends SimpleTile {
         this._date = this._entry.timestamp ? new Date(this._entry.timestamp) : null;
         this._isContinuation = false;
         this._reactions = null;
-        if (this._entry.annotations) {
+        if (this._entry.annotations || this._entry.pendingAnnotations) {
             this._updateReactions();
         }
     }
@@ -135,8 +135,8 @@ export class BaseMessageTile extends SimpleTile {
     }
 
     _updateReactions() {
-        const {annotations} = this._entry;
-        if (!annotations) {
+        const {annotations, pendingAnnotations} = this._entry;
+        if (!annotations && !pendingAnnotations) {
             if (this._reactions) {
                 this._reactions = null;
             }
@@ -144,7 +144,7 @@ export class BaseMessageTile extends SimpleTile {
             if (!this._reactions) {
                 this._reactions = new ReactionsViewModel(this);
             }
-            this._reactions.update(annotations);
+            this._reactions.update(annotations, pendingAnnotations);
         }
     }
 }
diff --git a/src/matrix/room/timeline/PendingAnnotations.js b/src/matrix/room/timeline/PendingAnnotations.js
new file mode 100644
index 00000000..b2b3ea57
--- /dev/null
+++ b/src/matrix/room/timeline/PendingAnnotations.js
@@ -0,0 +1,69 @@
+/*
+Copyright 2021 The Matrix.org Foundation C.I.C.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+import {getRelationFromContent} from "./relations.js";
+
+class PendingAnnotations {
+    constructor() {
+        this.aggregatedAnnotations = new Map();
+        this._entries = [];
+    }
+
+    add(pendingEventEntry) {
+        const relation = getRelationFromContent(pendingEventEntry.content);
+        const key = relation.key;
+        if (!key) {
+            return;
+        }
+        const count = this.aggregatedAnnotations.get(key) || 0;
+        //const addend = pendingEventEntry.isRedacted ? -1 : 1;
+        //this.aggregatedAnnotations.set(key, count + addend);
+        this.aggregatedAnnotations.set(key, count + 1);
+        this._entries.push(pendingEventEntry);
+    }
+
+    remove(pendingEventEntry) {
+        const idx = this._entries.indexOf(pendingEventEntry);
+        if (idx === -1) {
+            return;
+        }
+        this._entries.splice(idx, 1);
+        const relation = getRelationFromContent(pendingEventEntry.content);
+        const key = relation.key;
+        let count = this.aggregatedAnnotations.get(key);
+        if (count !== undefined) {
+            count -= 1;
+            if (count <= 0) {
+                this.aggregatedAnnotations.delete(key);
+            } else {
+                this.aggregatedAnnotations.set(key, count);
+            }
+        }
+    }
+
+    findForKey(key) {
+        return this._entries.find(e => {
+            const relation = getRelationFromContent(e.content);
+            if (relation.key === key) {
+                return e;
+            }
+        });
+    }
+
+    get isEmpty() {
+        return this._entries.length;
+    }
+}
\ No newline at end of file
diff --git a/src/matrix/room/timeline/entries/BaseEventEntry.js b/src/matrix/room/timeline/entries/BaseEventEntry.js
index a036e8c6..6e3254e8 100644
--- a/src/matrix/room/timeline/entries/BaseEventEntry.js
+++ b/src/matrix/room/timeline/entries/BaseEventEntry.js
@@ -16,12 +16,14 @@ limitations under the License.
 
 import {BaseEntry} from "./BaseEntry.js";
 import {REDACTION_TYPE} from "../../common.js";
-import {createAnnotation} from "../relations.js";
+import {createAnnotation, getRelationFromContent, ANNOTATION_RELATION_TYPE} from "../relations.js";
+import {PendingAnnotations} from "../PendingAnnotations.js";
 
 export class BaseEventEntry extends BaseEntry {
     constructor(fragmentIdComparer) {
         super(fragmentIdComparer);
         this._pendingRedactions = null;
+        this._pendingAnnotations = null;
     }
 
     get isRedacting() {
@@ -52,6 +54,15 @@ export class BaseEventEntry extends BaseEntry {
             if (this._pendingRedactions.length === 1) {
                 return "isRedacted";
             }
+        } else {
+            const relation = getRelationFromContent(entry.content);
+            if (relation && relation.rel_type === ANNOTATION_RELATION_TYPE) {
+                if (!this._pendingAnnotations) {
+                    this._pendingAnnotations = new PendingAnnotations();
+                }
+                this._pendingAnnotations.add(entry);
+                return "pendingAnnotations";
+            }
         }
     }
     
@@ -69,6 +80,15 @@ export class BaseEventEntry extends BaseEntry {
                     return "isRedacted";
                 }
             }
+        } else {
+            const relation = getRelationFromContent(entry.content);
+            if (relation && relation.rel_type === ANNOTATION_RELATION_TYPE && this._pendingAnnotations) {
+                this._pendingAnnotations.remove(entry);
+                if (this._pendingAnnotations.isEmpty) {
+                    this._pendingAnnotations = null;
+                }
+                return "pendingAnnotations";
+            }
         }
     }
 
@@ -85,4 +105,13 @@ export class BaseEventEntry extends BaseEntry {
     annotate(key) {
         return createAnnotation(this.id, key);
     }
-}
+
+    get pendingAnnotations() {
+        return this._pendingAnnotations?.aggregatedAnnotations;
+    }
+
+    async getOwnAnnotationId(room, key) {
+        const pendingEvent = this._pendingAnnotations?.findForKey(key);
+        return pendingEvent?.id;
+    }
+}
\ No newline at end of file
diff --git a/src/matrix/room/timeline/entries/EventEntry.js b/src/matrix/room/timeline/entries/EventEntry.js
index 311cea8c..a106ef7b 100644
--- a/src/matrix/room/timeline/entries/EventEntry.js
+++ b/src/matrix/room/timeline/entries/EventEntry.js
@@ -131,7 +131,12 @@ export class EventEntry extends BaseEventEntry {
         return this._eventEntry.annotations;
     }
 
-    getOwnAnnotationId(room, key) {
-        return room.getOwnAnnotationEventId(this.id, key);
+    async getOwnAnnotationId(room, key) {
+        const localId = await super.getOwnAnnotationId(room, key);
+        if (localId) {
+            return localId;
+        } else {
+            return room.getOwnAnnotationEventId(this.id, key);
+        }
     }
 }
\ No newline at end of file
diff --git a/src/platform/web/ui/session/room/timeline/ReactionsView.js b/src/platform/web/ui/session/room/timeline/ReactionsView.js
index c1250683..33a34c9f 100644
--- a/src/platform/web/ui/session/room/timeline/ReactionsView.js
+++ b/src/platform/web/ui/session/room/timeline/ReactionsView.js
@@ -33,7 +33,7 @@ class ReactionView extends TemplateView {
     render(t, vm) {
         const haveReacted = vm => vm.haveReacted;
         return t.button({
-            className: {haveReacted},
+            className: {haveReacted, isPending: vm => vm.isPending},
         }, [vm.key, " ", vm => `${vm.count}`]);
     }