diff --git a/app/controllers/notifications_controller.rb b/app/controllers/notifications_controller.rb
index 002385cc6ef..e8e0d111699 100644
--- a/app/controllers/notifications_controller.rb
+++ b/app/controllers/notifications_controller.rb
@@ -146,6 +146,10 @@ class NotificationsController < ApplicationController
     render json: success_json
   end
 
+  def totals
+    render_serialized(current_user, UserNotificationTotalSerializer, root: false)
+  end
+
   private
 
   def set_notification
diff --git a/app/models/topic_tracking_state.rb b/app/models/topic_tracking_state.rb
index 71a04824bdd..770ded22e4e 100644
--- a/app/models/topic_tracking_state.rb
+++ b/app/models/topic_tracking_state.rb
@@ -577,6 +577,44 @@ class TopicTrackingState
     post.publish_change_to_clients!(:read, opts)
   end
 
+  def self.report_count_by_type(user, type:)
+    tag_ids = muted_tag_ids(user)
+    sql =
+      report_raw_sql(
+        topic_id: nil,
+        skip_unread: type == "new",
+        skip_new: type == "unread",
+        skip_order: true,
+        staff: user.staff?,
+        admin: user.admin?,
+        whisperer: user.whisperer?,
+        user: user,
+        muted_tag_ids: tag_ids,
+      )
+    sql = tags_included_wrapped_sql(sql)
+
+    DB.query(
+      sql + "\n\n LIMIT :max_topics",
+      {
+        user_id: user.id,
+        topic_id: nil,
+        min_new_topic_date: Time.at(SiteSetting.min_new_topics_time).to_datetime,
+        max_topics: TopicTrackingState::MAX_TOPICS,
+        user_first_unread_at: user.user_stat.first_unread_at,
+      }.merge(treat_as_new_topic_params),
+    ).count
+  end
+
+  def self.report_totals(user)
+    if user.new_new_view_enabled?
+      { new: report(user).count }
+    else
+      new = report_count_by_type(user, type: "new")
+      unread = report_count_by_type(user, type: "unread")
+      { new: new, unread: unread }
+    end
+  end
+
   def self.secure_category_group_ids(topic)
     category = topic.category
 
diff --git a/app/serializers/user_notification_total_serializer.rb b/app/serializers/user_notification_total_serializer.rb
new file mode 100644
index 00000000000..5faecb530b8
--- /dev/null
+++ b/app/serializers/user_notification_total_serializer.rb
@@ -0,0 +1,65 @@
+# frozen_string_literal: true
+
+class UserNotificationTotalSerializer < ApplicationSerializer
+  attributes :username,
+             :unread_notifications,
+             :unread_personal_messages,
+             :unseen_reviewables,
+             :topic_tracking,
+             :group_inboxes
+
+  def unread_notifications
+    object.all_unread_notifications_count - new_personal_messages_notifications_count
+  end
+
+  def include_unread_personal_messages?
+    object.in_any_groups?(SiteSetting.personal_message_enabled_groups_map)
+  end
+
+  def unread_personal_messages
+    new_personal_messages_notifications_count
+  end
+
+  def include_unseen_reviewables?
+    scope.user.staff?
+  end
+
+  def unseen_reviewables
+    Reviewable.unseen_reviewable_count(object)
+  end
+
+  def topic_tracking
+    TopicTrackingState.report_totals(object)
+  end
+
+  def group_inboxes
+    group_inbox_data =
+      Notification
+        .unread
+        .where(
+          user_id: scope.user.id,
+          notification_type: Notification.types[:group_message_summary],
+        )
+        .pluck(:data)
+
+    results = []
+
+    return results if group_inbox_data.blank?
+
+    group_inbox_data.map do |json|
+      data = JSON.parse(json, symbolize_names: true)
+
+      results << {
+        group_id: data[:group_id],
+        group_name: data[:group_name],
+        count: data[:inbox_count],
+      }
+    end
+
+    results
+  end
+
+  def new_personal_messages_notifications_count
+    @new_personal_messages_notifications_count ||= object.new_personal_messages_notifications_count
+  end
+end
diff --git a/config/routes.rb b/config/routes.rb
index 11bd8b70bfd..823a5d1dfa5 100644
--- a/config/routes.rb
+++ b/config/routes.rb
@@ -1129,6 +1129,7 @@ Discourse::Application.routes.draw do
         # creating an alias cause the api was extended to mark a single notification
         # this allows us to cleanly target it
         put "read" => "notifications#mark_read"
+        get "totals" => "notifications#totals"
       end
     end
 
diff --git a/plugins/chat/lib/chat/channel_fetcher.rb b/plugins/chat/lib/chat/channel_fetcher.rb
index 3a557af0dca..73e79c9f0eb 100644
--- a/plugins/chat/lib/chat/channel_fetcher.rb
+++ b/plugins/chat/lib/chat/channel_fetcher.rb
@@ -253,6 +253,20 @@ module Chat
       ).report
     end
 
+    def self.unreads_total(guardian)
+      result = 0
+
+      public_channels = secured_public_channels(guardian, status: :open, following: true)
+      publics = tracking_state(public_channels.map(&:id), guardian, include_threads: true)
+      publics.channel_tracking.each_value { |channel_info| result += channel_info[:mention_count] }
+
+      direct_message_channels = secured_direct_message_channels(guardian.user.id, guardian)
+      directs = tracking_state(direct_message_channels.map(&:id), guardian)
+      directs.channel_tracking.each_value { |channel_info| result += channel_info[:unread_count] }
+
+      result
+    end
+
     def self.find_with_access_check(channel_id_or_slug, guardian)
       base_channel_relation = Chat::Channel.includes(:chatable)
 
diff --git a/plugins/chat/plugin.rb b/plugins/chat/plugin.rb
index 1e26ecc3575..b2728cb7473 100644
--- a/plugins/chat/plugin.rb
+++ b/plugins/chat/plugin.rb
@@ -246,6 +246,16 @@ after_initialize do
       .map { |row| { channel_id: row[0], data: row[1], thread_id: row[2] } }
   end
 
+  add_to_serializer(
+    :user_notification_total,
+    :chat_notifications,
+    include_condition: -> do
+      return @has_chat_enabled if defined?(@has_chat_enabled)
+      @has_chat_enabled =
+        SiteSetting.chat_enabled && scope.can_chat? && object.user_option.chat_enabled
+    end,
+  ) { Chat::ChannelFetcher.unreads_total(self.scope) }
+
   add_to_serializer(:user_option, :chat_enabled) { object.chat_enabled }
 
   add_to_serializer(
diff --git a/plugins/chat/spec/lib/chat/channel_fetcher_spec.rb b/plugins/chat/spec/lib/chat/channel_fetcher_spec.rb
index 4664f7f3185..ad86be89c6f 100644
--- a/plugins/chat/spec/lib/chat/channel_fetcher_spec.rb
+++ b/plugins/chat/spec/lib/chat/channel_fetcher_spec.rb
@@ -415,6 +415,63 @@ describe Chat::ChannelFetcher do
     end
   end
 
+  describe ".unreads_total" do
+    it "returns correct totals for DMs and mentions" do
+      result = described_class.unreads_total(guardian)
+
+      expect(result).to eq(0)
+
+      Fabricate(
+        :user_chat_channel_membership_for_dm,
+        chat_channel: direct_message_channel1,
+        user: user1,
+        following: true,
+      )
+      Chat::DirectMessageUser.create!(direct_message: dm_channel1, user: user1)
+      Chat::DirectMessageUser.create!(direct_message: dm_channel1, user: user2)
+      Fabricate(
+        :user_chat_channel_membership_for_dm,
+        chat_channel: direct_message_channel2,
+        user: user1,
+        following: true,
+      )
+      Chat::DirectMessageUser.create!(direct_message: dm_channel2, user: user1)
+      Chat::DirectMessageUser.create!(direct_message: dm_channel2, user: user2)
+
+      dm_1 = Fabricate(:chat_message, user: user1, chat_channel: direct_message_channel1)
+      dm_2 = Fabricate(:chat_message, user: user1, chat_channel: direct_message_channel2)
+
+      direct_message_channel1.update!(last_message: dm_1)
+      direct_message_channel1.last_message.update!(created_at: 1.day.ago)
+      direct_message_channel2.update!(last_message: dm_2)
+      direct_message_channel2.last_message.update!(created_at: 1.hour.ago)
+
+      result = described_class.unreads_total(guardian)
+      expect(result).to eq(2)
+
+      membership =
+        Fabricate(:user_chat_channel_membership, chat_channel: category_channel, user: user1)
+      message =
+        Fabricate(:chat_message, chat_channel: category_channel, message: "bonjour", user: user2)
+      notification =
+        Notification.create!(
+          notification_type: Notification.types[:chat_mention],
+          user_id: user1.id,
+          data: { chat_message_id: message.id, chat_channel_id: category_channel.id }.to_json,
+        )
+      Chat::UserMention.create!(notifications: [notification], user: user1, chat_message: message)
+
+      result = described_class.unreads_total(guardian)
+      expect(result).to eq(3) # 2 DMs + 1 mention
+
+      # mark mention as read
+      membership.update!(last_read_message_id: message.id)
+
+      result = described_class.unreads_total(guardian)
+      expect(result).to eq(2) # only 2 DMs left unread
+    end
+  end
+
   describe ".find_with_access_check" do
     it "raises NotFound if the channel does not exist" do
       category_channel.destroy!
diff --git a/plugins/chat/spec/requests/core_ext/notifications_controller_spec.rb b/plugins/chat/spec/requests/core_ext/notifications_controller_spec.rb
new file mode 100644
index 00000000000..ecd9bfa1238
--- /dev/null
+++ b/plugins/chat/spec/requests/core_ext/notifications_controller_spec.rb
@@ -0,0 +1,59 @@
+# frozen_string_literal: true
+
+RSpec.describe NotificationsController do
+  context "when logged in" do
+    fab!(:chatters) { Fabricate(:group) }
+    fab!(:user) { Fabricate(:user, group_ids: [chatters.id]) }
+    fab!(:user2) { Fabricate(:user, group_ids: [chatters.id]) }
+    fab!(:dm1) { Fabricate(:direct_message) }
+    fab!(:direct_message_channel1) { Fabricate(:direct_message_channel, chatable: dm1) }
+    fab!(:dm2) { Fabricate(:direct_message) }
+    fab!(:direct_message_channel2) { Fabricate(:direct_message_channel, chatable: dm2) }
+
+    before do
+      Jobs.run_immediately!
+      SiteSetting.chat_enabled = true
+      SiteSetting.chat_allowed_groups = [chatters.id]
+      sign_in(user)
+    end
+
+    def create_dm(user, channel, dm)
+      Fabricate(
+        :user_chat_channel_membership_for_dm,
+        chat_channel: channel,
+        user: user,
+        following: true,
+      )
+      Chat::DirectMessageUser.create!(direct_message: dm, user: user)
+
+      msg = Fabricate(:chat_message, user: user, chat_channel: channel)
+
+      channel.update!(last_message: msg)
+      channel.last_message.update!(created_at: 1.day.ago)
+    end
+
+    describe "#totals" do
+      it "has a total of 0 chat notifications by default" do
+        get "/notifications/totals.json"
+
+        expect(response.status).to eq(200)
+        expect(response.parsed_body["chat_notifications"]).to eq(0)
+      end
+
+      it "returns the correct chat notifications count for unread DMs" do
+        create_dm(user, direct_message_channel1, dm1)
+
+        get "/notifications/totals.json"
+
+        expect(response.status).to eq(200)
+        expect(response.parsed_body["chat_notifications"]).to eq(1)
+
+        create_dm(user, direct_message_channel2, dm2)
+
+        get "/notifications/totals.json"
+
+        expect(response.parsed_body["chat_notifications"]).to eq(2)
+      end
+    end
+  end
+end
diff --git a/spec/models/topic_tracking_state_spec.rb b/spec/models/topic_tracking_state_spec.rb
index 42d778b0e46..c93fee99ad4 100644
--- a/spec/models/topic_tracking_state_spec.rb
+++ b/spec/models/topic_tracking_state_spec.rb
@@ -755,6 +755,89 @@ RSpec.describe TopicTrackingState do
     end
   end
 
+  describe ".report_totals" do
+    fab!(:user2) { Fabricate(:user) }
+
+    it "correctly returns new/unread totals" do
+      report = TopicTrackingState.report_totals(user)
+      expect(report).to eq({ new: 0, unread: 0 })
+
+      post.topic.notifier.watch_topic!(post.topic.user_id)
+
+      report = TopicTrackingState.report_totals(user)
+      expect(report).to eq({ new: 1, unread: 0 })
+
+      create_post(user: user, topic: post.topic)
+
+      # when user replies, they have 0 new count
+      report = TopicTrackingState.report_totals(user)
+      expect(report).to eq({ new: 0, unread: 0 })
+
+      # when we reply the poster will have an unread item
+      report = TopicTrackingState.report_totals(post.user)
+      expect(report).to eq({ new: 0, unread: 1 })
+
+      create_post(user: user2, topic: post.topic)
+
+      # when a third user replies, the original user should have an unread item
+      report = TopicTrackingState.report_totals(user)
+      expect(report).to eq({ new: 0, unread: 1 })
+
+      # the post user still has one unread
+      report = TopicTrackingState.report_totals(post.user)
+      expect(report).to eq({ new: 0, unread: 1 })
+
+      post2 = create_post
+      post2.topic.notifier.watch_topic!(user.id)
+
+      # watching another new topic bumps the new count
+      report = TopicTrackingState.report_totals(user)
+      expect(report).to eq({ new: 1, unread: 1 })
+    end
+
+    it "respects treat_as_new_topic_start_date user option" do
+      report = TopicTrackingState.report_totals(user)
+      expect(report).to eq({ new: 0, unread: 0 })
+
+      post.topic.notifier.watch_topic!(post.topic.user_id)
+
+      report = TopicTrackingState.report_totals(user)
+      expect(report).to eq({ new: 1, unread: 0 })
+
+      user.user_option.new_topic_duration_minutes = 5
+      user.user_option.save
+      post.topic.created_at = 10.minutes.ago
+      post.topic.save
+
+      report = TopicTrackingState.report_totals(user)
+      expect(report).to eq({ new: 0, unread: 0 })
+    end
+
+    it "respects new_new_view_enabled" do
+      new_new_group = Fabricate(:group)
+      SiteSetting.experimental_new_new_view_groups = new_new_group.name
+      user.groups << new_new_group
+
+      report = TopicTrackingState.report_totals(user)
+      expect(report).to eq({ new: 0 })
+
+      post.topic.notifier.watch_topic!(post.topic.user_id)
+
+      post2 = create_post
+      Fabricate(:post, topic: post2.topic)
+
+      tracking = {
+        notification_level: TopicUser.notification_levels[:tracking],
+        last_read_post_number: 1,
+      }
+
+      TopicUser.change(user.id, post2.topic_id, tracking)
+
+      report = TopicTrackingState.report_totals(user)
+      expect(report).to eq({ new: 2 })
+    end
+  end
+
   describe ".publish_recover" do
     include_examples("publishes message to right groups and users", "/recover", :publish_recover)
     include_examples("does not publish message for private topics", :publish_recover)
diff --git a/spec/requests/notifications_controller_spec.rb b/spec/requests/notifications_controller_spec.rb
index 1c725999536..8634c32b1c5 100644
--- a/spec/requests/notifications_controller_spec.rb
+++ b/spec/requests/notifications_controller_spec.rb
@@ -618,5 +618,12 @@ RSpec.describe NotificationsController do
         delete_notification(403, :to)
       end
     end
+
+    describe "#totals" do
+      it "can't see notification totals" do
+        get "/notifications/totals.json"
+        expect(response.status).to eq(403)
+      end
+    end
   end
 end
diff --git a/spec/serializers/user_notification_total_serializer_spec.rb b/spec/serializers/user_notification_total_serializer_spec.rb
new file mode 100644
index 00000000000..cf850763f58
--- /dev/null
+++ b/spec/serializers/user_notification_total_serializer_spec.rb
@@ -0,0 +1,61 @@
+# frozen_string_literal: true
+
+RSpec.describe UserNotificationTotalSerializer do
+  fab!(:user) { Fabricate(:user, trust_level: 3) }
+
+  fab!(:notification) { Fabricate(:notification, user: user, read: false) }
+  fab!(:pm_notification) do
+    Fabricate(:notification, user: user, notification_type: Notification.types[:private_message])
+  end
+  fab!(:pm_notification2) do
+    Fabricate(:notification, user: user, notification_type: Notification.types[:private_message])
+  end
+  fab!(:group_message_notification) do
+    Fabricate(
+      :notification,
+      user: user,
+      notification_type: Notification.types[:group_message_summary],
+      data: { group_id: 1, group_name: "Group", inbox_count: 5 }.to_json,
+    )
+  end
+  fab!(:reviewable)
+
+  let(:serializer) { described_class.new(user, scope: Guardian.new(user), root: false) }
+  let(:serialized_data) { serializer.as_json }
+
+  it "includes the user's unread regular notifications count" do
+    # notification + group_message_notification - pm_notifications
+    expect(serialized_data[:unread_notifications]).to eq(2)
+  end
+
+  it "includes the user's unread private messages count" do
+    expect(serialized_data[:unread_personal_messages]).to eq(2)
+  end
+
+  context "when the user has PMs disabled" do
+    it "does not include the user's unread private messages count" do
+      SiteSetting.personal_message_enabled_groups = Group::AUTO_GROUPS[:trust_level_4]
+      expect(serialized_data).not_to have_key(:unread_personal_messages)
+    end
+  end
+
+  it "includes group inbox notification counts" do
+    expect(serialized_data[:group_inboxes]).to contain_exactly(
+      { group_id: 1, group_name: "Group", count: 5 },
+    )
+  end
+
+  context "when the user is staff" do
+    before { user.update!(admin: true) }
+
+    it "includes the count of unseen reviewables" do
+      expect(serialized_data[:unseen_reviewables]).to eq(1)
+    end
+  end
+
+  context "when the user is not staff" do
+    it "does not include unseen reviewables counts" do
+      expect(serialized_data).not_to have_key(:unseen_reviewables)
+    end
+  end
+end