diff --git a/ts/components/conversation/media-gallery/groupMessagesByDate.ts b/ts/components/conversation/media-gallery/groupMessagesByDate.ts
new file mode 100644
index 000000000..10a869c06
--- /dev/null
+++ b/ts/components/conversation/media-gallery/groupMessagesByDate.ts
@@ -0,0 +1,52 @@
+import moment from 'moment';
+import { groupBy, sortBy } from 'lodash';
+
+import { Message } from './propTypes/Message';
+
+
+export const groupMessagesByDate = (timestamp: number, messages: Array<Message>): any => {
+  const referenceDateTime = moment.utc(timestamp);
+  const today = moment(referenceDateTime).startOf('day');
+  const yesterday = moment(referenceDateTime).subtract(1, 'day').startOf('day');
+  const thisWeek = moment(referenceDateTime).startOf('week');
+  const thisMonth = moment(referenceDateTime).startOf('month');
+
+  const sorted = sortBy(messages, (message) => -message.received_at);
+  const annotations = sorted.map((message) => {
+    const date = moment(message.received_at);
+
+    if (date.isAfter(today)) {
+      return {
+        order: 0,
+        label: 'today',
+        message,
+      };
+    } else if (date.isAfter(yesterday)) {
+      return {
+        order: 1,
+        label: 'yesterday',
+        message,
+      };
+    } else if (date.isAfter(thisWeek)) {
+      return {
+        order: 2,
+        label: 'thisWeek',
+        message,
+      };
+    } else if (date.isAfter(thisMonth)) {
+      return {
+        order: 3,
+        label: 'thisMonth',
+        message,
+      };
+    }
+
+    return {
+      order: (date.year() * 100) + date.month(),
+      label: 'yearMonth',
+      message,
+    };
+  });
+
+  return groupBy(annotations, 'label');
+};
diff --git a/ts/test/components/media-gallery/groupMessagesByDate.ts b/ts/test/components/media-gallery/groupMessagesByDate.ts
new file mode 100644
index 000000000..6f0d9dbb5
--- /dev/null
+++ b/ts/test/components/media-gallery/groupMessagesByDate.ts
@@ -0,0 +1,183 @@
+import 'mocha';
+import { assert } from 'chai';
+
+import { groupMessagesByDate } from
+  '../../../components/conversation/media-gallery/groupMessagesByDate';
+import { Message } from
+  '../../../components/conversation/media-gallery/propTypes/Message';
+
+
+const toMessage = (date: Date): Message => ({
+  id: date.toUTCString(),
+  received_at: date.getTime(),
+  attachments: [],
+});
+
+describe('groupMessagesByDate', () => {
+  it('should group messages', () => {
+    const referenceTime = new Date('2018-04-12T18:00Z').getTime();
+    const input: Array<Message> = [
+      // Today
+      toMessage(new Date('2018-04-12T12:00Z')),
+      toMessage(new Date('2018-04-12T07:00Z')),
+      toMessage(new Date('2018-04-12T00:01Z')),
+      // This week
+      toMessage(new Date('2018-04-11T23:59Z')),
+      toMessage(new Date('2018-04-09T00:01Z')),
+      // This month
+      toMessage(new Date('2018-04-08T23:59Z')),
+      toMessage(new Date('2018-04-05T09:00Z')),
+      toMessage(new Date('2018-04-01T00:01Z')),
+      // March 2018
+      toMessage(new Date('2018-03-31T23:59Z')),
+      toMessage(new Date('2018-03-28T14:00Z')),
+      toMessage(new Date('2018-03-01T14:00Z')),
+      // February 2011
+      toMessage(new Date('2011-02-28T23:59Z')),
+      toMessage(new Date('2011-02-15T10:00Z')),
+      toMessage(new Date('2011-02-01T10:00Z')),
+    ];
+
+    const expected = {
+      today: [
+        {
+          order: 0,
+          label: 'today',
+          message: {
+            id: 'Thu, 12 Apr 2018 12:00:00 GMT',
+            received_at: 1523534400000,
+            attachments: [],
+          },
+        },
+        {
+          order: 0,
+          label: 'today',
+          message: {
+            id: 'Thu, 12 Apr 2018 07:00:00 GMT',
+            received_at: 1523516400000,
+            attachments: [],
+          },
+        },
+        {
+          order: 0,
+          label: 'today',
+          message: {
+            id: 'Thu, 12 Apr 2018 00:01:00 GMT',
+            received_at: 1523491260000,
+            attachments: [],
+          },
+        },
+      ],
+      yesterday: [
+        {
+          order: 1,
+          label: 'yesterday',
+          message: {
+            id: 'Wed, 11 Apr 2018 23:59:00 GMT',
+            received_at: 1523491140000,
+            attachments: [],
+          },
+        },
+      ],
+      thisWeek: [
+        {
+          order: 2,
+          label: 'thisWeek',
+          message: {
+            id: 'Mon, 09 Apr 2018 00:01:00 GMT',
+            received_at: 1523232060000,
+            attachments: [],
+          },
+        },
+        {
+          order: 2,
+          label: 'thisWeek',
+          message: {
+            id: 'Sun, 08 Apr 2018 23:59:00 GMT',
+            received_at: 1523231940000,
+            attachments: [],
+          },
+        },
+      ],
+      thisMonth: [
+        {
+          order: 3,
+          label: 'thisMonth',
+          message: {
+            id: 'Thu, 05 Apr 2018 09:00:00 GMT',
+            received_at: 1522918800000,
+            attachments: [],
+          },
+        },
+        {
+          order: 3,
+          label: 'thisMonth',
+          message: {
+            id: 'Sun, 01 Apr 2018 00:01:00 GMT',
+            received_at: 1522540860000,
+            attachments: [],
+          },
+        },
+      ],
+      yearMonth: [
+        {
+          order: 201802,
+          label: 'yearMonth',
+          message: {
+            id: 'Sat, 31 Mar 2018 23:59:00 GMT',
+            received_at: 1522540740000,
+            attachments: [],
+          },
+        },
+        {
+          order: 201802,
+          label: 'yearMonth',
+          message: {
+            id: 'Wed, 28 Mar 2018 14:00:00 GMT',
+            received_at: 1522245600000,
+            attachments: [],
+          },
+        },
+        {
+          order: 201802,
+          label: 'yearMonth',
+          message: {
+            id: 'Thu, 01 Mar 2018 14:00:00 GMT',
+            received_at: 1519912800000,
+            attachments: [],
+          },
+        },
+        {
+          order: 201101,
+          label: 'yearMonth',
+          message: {
+            id: 'Mon, 28 Feb 2011 23:59:00 GMT',
+            received_at: 1298937540000,
+            attachments: [],
+          },
+        },
+        {
+          order: 201101,
+          label: 'yearMonth',
+          message: {
+            id: 'Tue, 15 Feb 2011 10:00:00 GMT',
+            received_at: 1297764000000,
+            attachments: [],
+          },
+        },
+        {
+          order: 201101,
+          label: 'yearMonth',
+          message: {
+            id: 'Tue, 01 Feb 2011 10:00:00 GMT',
+            received_at: 1296554400000,
+            attachments: [],
+          },
+        },
+      ],
+    };
+
+    const actual = groupMessagesByDate(referenceTime, input);
+    assert.deepEqual(actual, expected);
+  });
+});