diff --git a/src/api/friends/friendCategory.helpers.test.ts b/src/api/friends/friendCategory.helpers.test.ts
new file mode 100644
index 0000000..740769d
--- /dev/null
+++ b/src/api/friends/friendCategory.helpers.test.ts
@@ -0,0 +1,53 @@
+import { describe, expect, it } from 'vitest';
+import { MessengerFriend } from './MessengerFriend';
+import { countFriendsByCategory, filterFriendsByCategory } from './friendCategory.helpers';
+
+const makeFriend = (id: number, categoryId: number): MessengerFriend =>
+{
+    const friend = new MessengerFriend();
+    friend.id = id;
+    friend.categoryId = categoryId;
+    return friend;
+};
+
+describe('filterFriendsByCategory', () =>
+{
+    const friends = [ makeFriend(1, 0), makeFriend(2, 5), makeFriend(3, 5), makeFriend(4, 8) ];
+
+    it('returns all friends when categoryId is 0 (All)', () =>
+    {
+        expect(filterFriendsByCategory(friends, 0)).toHaveLength(4);
+    });
+
+    it('returns only the friends in the given category', () =>
+    {
+        expect(filterFriendsByCategory(friends, 5).map(f => f.id)).toEqual([ 2, 3 ]);
+    });
+
+    it('returns an empty array for a category with no members', () =>
+    {
+        expect(filterFriendsByCategory(friends, 99)).toEqual([]);
+    });
+
+    it('is null-safe', () =>
+    {
+        expect(filterFriendsByCategory(null, 5)).toEqual([]);
+    });
+});
+
+describe('countFriendsByCategory', () =>
+{
+    const friends = [ makeFriend(1, 0), makeFriend(2, 5), makeFriend(3, 5) ];
+
+    it('counts members per category id', () =>
+    {
+        const counts = countFriendsByCategory(friends);
+        expect(counts.get(0)).toBe(1);
+        expect(counts.get(5)).toBe(2);
+    });
+
+    it('is null-safe', () =>
+    {
+        expect(countFriendsByCategory(null).size).toBe(0);
+    });
+});
diff --git a/src/api/friends/friendCategory.helpers.ts b/src/api/friends/friendCategory.helpers.ts
new file mode 100644
index 0000000..0c29e91
--- /dev/null
+++ b/src/api/friends/friendCategory.helpers.ts
@@ -0,0 +1,32 @@
+import { MessengerFriend } from './MessengerFriend';
+
+/**
+ * Filter a friend list to a single category. categoryId 0 means
+ * "All" (no filtering) and returns the list unchanged.
+ */
+export const filterFriendsByCategory = (friends: MessengerFriend[], categoryId: number): MessengerFriend[] =>
+{
+    if(!friends) return [];
+
+    if(!categoryId) return friends;
+
+    return friends.filter(friend => (friend.categoryId === categoryId));
+};
+
+/**
+ * Count how many friends belong to each category id. Used to render
+ * member counts on the group chips.
+ */
+export const countFriendsByCategory = (friends: MessengerFriend[]): Map<number, number> =>
+{
+    const counts = new Map<number, number>();
+
+    if(!friends) return counts;
+
+    for(const friend of friends)
+    {
+        counts.set(friend.categoryId, (counts.get(friend.categoryId) ?? 0) + 1);
+    }
+
+    return counts;
+};
diff --git a/src/api/friends/index.ts b/src/api/friends/index.ts
index ce1ed60..621bc50 100644
--- a/src/api/friends/index.ts
+++ b/src/api/friends/index.ts
@@ -1,3 +1,4 @@
+export * from './friendCategory.helpers';
 export * from './GetGroupChatData';
 export * from './IGroupChatData';
 export * from './MessengerFriend';