diff --git a/app/models/journal/caused_by_total_percent_complete_mode_changed_to_work_weighted_average.rb b/app/models/journal/caused_by_total_percent_complete_mode_changed_to_work_weighted_average.rb
new file mode 100644
index 000000000000..b1d2ce41a29c
--- /dev/null
+++ b/app/models/journal/caused_by_total_percent_complete_mode_changed_to_work_weighted_average.rb
@@ -0,0 +1,33 @@
+#-- copyright
+# OpenProject is an open source project management software.
+# Copyright (C) the OpenProject GmbH
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version 3.
+#
+# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+# Copyright (C) 2006-2013 Jean-Philippe Lang
+# Copyright (C) 2010-2013 the ChiliProject Team
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+#
+# See COPYRIGHT and LICENSE files for more details.
+#++
+
+class Journal::CausedByTotalPercentCompleteModeChangedToWorkWeightedAverage < CauseOfChange::Base
+  def initialize
+    super("total_percent_complete_mode_changed_to_work_weighted_average")
+  end
+end
diff --git a/app/workers/work_packages/progress/apply_total_percent_complete_mode_change_job.rb b/app/workers/work_packages/progress/apply_total_percent_complete_mode_change_job.rb
new file mode 100644
index 000000000000..518d1004959a
--- /dev/null
+++ b/app/workers/work_packages/progress/apply_total_percent_complete_mode_change_job.rb
@@ -0,0 +1,143 @@
+#-- copyright
+# OpenProject is an open source project management software.
+# Copyright (C) the OpenProject GmbH
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version 3.
+#
+# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+# Copyright (C) 2006-2013 Jean-Philippe Lang
+# Copyright (C) 2010-2013 the ChiliProject Team
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+#
+# See COPYRIGHT and LICENSE files for more details.
+#++
+
+class WorkPackages::Progress::ApplyTotalPercentCompleteModeChangeJob < WorkPackages::Progress::Job
+  VALID_CAUSE_TYPES = %w[
+    total_percent_complete_mode_changed_to_work_weighted_average
+    total_percent_complete_mode_changed_to_simple_average
+  ].freeze
+
+  attr_reader :cause_type, :old_mode, :new_mode
+
+  # Updates the total % complete of all work packages after the total
+  # percent complete mode has been changed.
+  #
+  # It creates a journal entry with the System user describing the changes.
+  #
+  #
+  # Updates the total % complete of all work packages after the total
+  # percent complete mode has been changed.
+  #
+  # It creates a journal entry with the System user describing the changes.
+  #
+  # @param [String] old_mode The previous total percent complete mode
+  # @param [String] new_mode The new total percent complete mode
+  # @return [void]
+  def perform(cause_type:, old_mode:, new_mode:)
+    @cause_type = cause_type
+    @old_mode = old_mode
+    @new_mode = new_mode
+
+    with_temporary_total_percent_complete_table do
+      update_total_percent_complete
+      copy_total_percent_complete_values_to_work_packages_and_update_journals(journal_cause)
+    end
+  end
+
+  private
+
+  def update_total_percent_complete
+    case new_mode
+    when "work_weighted_average"
+      update_work_weighted_average
+    when "simple_average"
+      update_simple_average
+    else
+      raise ArgumentError, "Invalid total percent complete mode: #{new_mode}"
+    end
+  end
+
+  def update_work_weighted_average
+    execute(<<~SQL.squish)
+      UPDATE temp_wp_progress_values
+      SET total_p_complete = CASE
+        WHEN total_work IS NULL OR total_remaining_work IS NULL THEN NULL
+        WHEN total_work = 0 THEN NULL
+        ELSE ROUND(
+          ((total_work - total_remaining_work)::float / total_work) * 100
+        )
+      END
+      WHERE id IN (
+        SELECT ancestor_id
+        FROM work_package_hierarchies
+        GROUP BY ancestor_id
+        HAVING MAX(generations) > 0
+      )
+    SQL
+  end
+
+  def update_simple_average
+    execute(<<~SQL.squish)
+      UPDATE temp_wp_progress_values
+      SET derived_done_ratio = CASE
+        WHEN avg_ratios.avg_done_ratio IS NOT NULL THEN ROUND(avg_ratios.avg_done_ratio)
+        ELSE done_ratio
+      END
+      FROM (
+        SELECT wp_tree.ancestor_id AS id,
+               AVG(CASE
+                 WHEN wp_tree.generations = 1 THEN COALESCE(wp_progress.done_ratio, 0)
+                 ELSE NULL
+               END) AS avg_done_ratio
+        FROM work_package_hierarchies wp_tree
+          LEFT JOIN temp_wp_progress_values wp_progress ON wp_tree.descendant_id = wp_progress.id
+          LEFT JOIN statuses ON wp_progress.status_id = statuses.id
+        WHERE statuses.excluded_from_totals = FALSE
+        GROUP BY wp_tree.ancestor_id
+      ) avg_ratios
+      WHERE temp_wp_progress_values.id = avg_ratios.id
+      AND temp_wp_progress_values.id IN (
+        SELECT ancestor_id AS id
+        FROM work_package_hierarchies
+        GROUP BY id
+        HAVING MAX(generations) > 0
+      )
+    SQL
+  end
+
+  def journal_cause
+    assert_valid_cause_type!
+
+    @journal_cause ||=
+      case cause_type
+      when "total_percent_complete_mode_changed_to_work_weighted_average"
+        Journal::CausedByTotalPercentCompleteModeChangedToWorkWeightedAverage.new
+      when "total_percent_complete_mode_changed_to_simple_average"
+        Journal::CausedByTotalPercentCompleteModeChangedToSimpleAverage.new
+      else
+        raise "Unable to handle cause type #{cause_type.inspect}"
+      end
+  end
+
+  def assert_valid_cause_type!
+    unless VALID_CAUSE_TYPES.include?(cause_type)
+      raise ArgumentError, "Invalid cause type #{cause_type.inspect}. " \
+                           "Valid values are #{VALID_CAUSE_TYPES.inspect}"
+    end
+  end
+end
diff --git a/app/workers/work_packages/progress/sql_commands.rb b/app/workers/work_packages/progress/sql_commands.rb
index b00763d1098f..971d6556261d 100644
--- a/app/workers/work_packages/progress/sql_commands.rb
+++ b/app/workers/work_packages/progress/sql_commands.rb
@@ -60,6 +60,41 @@ def drop_temporary_progress_table
     SQL
   end
 
+  def with_temporary_total_percent_complete_table
+    WorkPackage.transaction do
+      case new_mode
+      when "work_weighted_average"
+        create_temporary_total_percent_complete_table_for_work_weighted_average_mode
+      when "simple_average"
+        create_temporary_total_percent_complete_table_for_simple_average_mode
+      else
+        raise ArgumentError, "Invalid total percent complete mode: #{new_mode}"
+      end
+
+      yield
+    ensure
+      drop_temporary_total_percent_complete_table
+    end
+  end
+
+  def create_temporary_total_percent_complete_table_for_work_weighted_average_mode
+    execute(<<~SQL.squish)
+      CREATE UNLOGGED TABLE temp_wp_progress_values
+      AS SELECT
+        id,
+        derived_estimated_hours as total_work,
+        derived_remaining_hours as total_remaining_work,
+        derived_done_ratio      as total_p_complete
+      FROM work_packages
+    SQL
+  end
+
+  def drop_temporary_total_percent_complete_table
+    execute(<<~SQL.squish)
+      DROP TABLE temp_wp_progress_values
+    SQL
+  end
+
   def derive_remaining_work_from_work_and_p_complete
     execute(<<~SQL.squish)
       UPDATE temp_wp_progress_values
@@ -170,6 +205,27 @@ def copy_progress_values_to_work_packages
     results.column_values(0)
   end
 
+  def copy_total_percent_complete_values_to_work_packages_and_update_journals(cause)
+    updated_work_package_ids = copy_total_percent_complete_values_to_work_packages
+    create_journals_for_updated_work_packages(updated_work_package_ids, cause:)
+  end
+
+  def copy_total_percent_complete_values_to_work_packages
+    results = execute(<<~SQL.squish)
+      UPDATE work_packages
+      SET derived_done_ratio = temp_wp_progress_values.total_p_complete,
+          lock_version       = lock_version + 1,
+          updated_at         = NOW()
+      FROM temp_wp_progress_values
+      WHERE work_packages.id = temp_wp_progress_values.id
+        AND (
+          work_packages.derived_done_ratio IS DISTINCT FROM temp_wp_progress_values.total_p_complete
+        )
+      RETURNING work_packages.id
+    SQL
+    results.column_values(0)
+  end
+
   def create_journals_for_updated_work_packages(updated_work_package_ids, cause:)
     WorkPackage.where(id: updated_work_package_ids).find_each do |work_package|
       Journals::CreateService
diff --git a/spec/workers/work_packages/progress/apply_total_percent_complete_mode_change_job_spec.rb b/spec/workers/work_packages/progress/apply_total_percent_complete_mode_change_job_spec.rb
new file mode 100644
index 000000000000..51e0cc38e06c
--- /dev/null
+++ b/spec/workers/work_packages/progress/apply_total_percent_complete_mode_change_job_spec.rb
@@ -0,0 +1,235 @@
+#-- copyright
+# OpenProject is an open source project management software.
+# Copyright (C) the OpenProject GmbH
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License version 3.
+#
+# OpenProject is a fork of ChiliProject, which is a fork of Redmine. The copyright follows:
+# Copyright (C) 2006-2013 Jean-Philippe Lang
+# Copyright (C) 2010-2013 the ChiliProject Team
+#
+# This program is free software; you can redistribute it and/or
+# modify it under the terms of the GNU General Public License
+# as published by the Free Software Foundation; either version 2
+# of the License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
+#
+# See COPYRIGHT and LICENSE files for more details.
+#++
+
+require "rails_helper"
+
+RSpec.describe WorkPackages::Progress::ApplyTotalPercentCompleteModeChangeJob do
+  shared_let(:author) { create(:user) }
+  shared_let(:priority) { create(:priority, name: "Normal") }
+  shared_let(:project) { create(:project, name: "Main project") }
+
+  # statuses for work-based mode
+  shared_let(:status_new) { create(:status, name: "New") }
+  shared_let(:status_wip) { create(:status, name: "In progress") }
+  shared_let(:status_closed) { create(:status, name: "Closed") }
+
+  # statuses for status-based mode
+  shared_let(:status_0p_todo) { create(:status, name: "To do (0%)", default_done_ratio: 0) }
+  shared_let(:status_40p_doing) { create(:status, name: "Doing (40%)", default_done_ratio: 40) }
+  shared_let(:status_100p_done) { create(:status, name: "Done (100%)", default_done_ratio: 100) }
+
+  # statuses for both work-based and status-based modes
+  shared_let(:status_excluded) { create(:status, :excluded_from_totals, name: "Excluded") }
+
+  before_all do
+    set_factory_default(:user, author)
+    set_factory_default(:priority, priority)
+    set_factory_default(:project, project)
+    set_factory_default(:project_with_types, project)
+    set_factory_default(:status, status_new)
+  end
+
+  subject(:job) { described_class }
+
+  def expect_performing_job_changes(from:, to:,
+                                    cause_type: "total_percent_complete_mode_changed_to_work_weighted_average",
+                                    old_mode: "simple_average",
+                                    new_mode: "work_weighted_average")
+    table = create_table(from)
+
+    job.perform_now(cause_type:, old_mode:, new_mode:)
+
+    table.work_packages.map(&:reload)
+    expect_work_packages(table.work_packages, to)
+
+    table.work_packages
+  end
+
+  context "when changing from simple average to work weighted average mode",
+          with_settings: { total_percent_complete_mode: "work_weighted_average" } do
+    context "on a single-level hierarchy" do
+      it "updates the total % complete of the work packages" do
+        expect_performing_job_changes(
+          old_mode: "simple_average",
+          new_mode: "work_weighted_average",
+          from: <<~TABLE,
+            hierarchy | work | ∑ work | remaining work | ∑ remaining work | % complete | ∑ % complete
+            flat_wp_1 |  10h |        |             6h |                  |        40% |
+            flat_wp_2 |  5h  |        |             3h |                  |        60% |
+          TABLE
+          to: <<~TABLE
+            subject   | work | ∑ work | remaining work | ∑ remaining work | % complete | ∑ % complete
+            flat_wp_1 |  10h |        |             6h |                  |        40% |
+            flat_wp_2 |  5h  |        |             3h |                  |        60% |
+          TABLE
+        )
+      end
+    end
+
+    context "on a two-level hierarchy with parents having total values" do
+      it "updates the total % complete of parent work packages" do
+        expect_performing_job_changes(
+          old_mode: "simple_average",
+          new_mode: "work_weighted_average",
+          from: <<~TABLE,
+            hierarchy | work | ∑ work | remaining work | ∑ remaining work | % complete | ∑ % complete
+            parent    |  10h |    30h |             6h |              6h  |        40% |          70%
+              child1  |  15h |        |             0h |                  |       100% |
+              child2  |      |        |                |                  |        40% |
+              child3  |   5h |        |             0h |                  |       100% |
+          TABLE
+          to: <<~TABLE
+            subject   | work | ∑ work | remaining work | ∑ remaining work | % complete | ∑ % complete
+            parent    |  10h |    30h |             6h |              6h  |        40% |          80%
+              child1  |  15h |        |             0h |                  |       100% |
+              child2  |      |        |                |                  |        40% |
+              child3  |   5h |        |             0h |                  |       100% |
+          TABLE
+        )
+      end
+    end
+
+    context "on a two-level hierarchy with only % complete values set" do
+      it "unsets the % complete value from parents" do
+        expect_performing_job_changes(
+          old_mode: "simple_average",
+          new_mode: "work_weighted_average",
+          from: <<~TABLE,
+            hierarchy | work | ∑ work | remaining work | ∑ remaining work | % complete | ∑ % complete
+            parent    |      |        |                |                  |        40% |          70%
+              child1  |      |        |                |                  |       100% |
+              child2  |      |        |                |                  |        40% |
+              child3  |      |        |                |                  |       100% |
+          TABLE
+          to: <<~TABLE
+            subject   | work | ∑ work | remaining work | ∑ remaining work | % complete | ∑ % complete
+            parent    |      |        |                |                  |        40% |
+              child1  |      |        |                |                  |       100% |
+              child2  |      |        |                |                  |        40% |
+              child3  |      |        |                |                  |       100% |
+          TABLE
+        )
+      end
+    end
+
+    context "on a multi-level hierarchy with only % complete values set" do
+      it "unsets the % complete value from parents" do
+        expect_performing_job_changes(
+          old_mode: "simple_average",
+          new_mode: "work_weighted_average",
+          from: <<~TABLE,
+            hierarchy       | work | ∑ work | remaining work | ∑ remaining work | % complete | ∑ % complete
+            parent          |      |        |                |                  |        40% |          63%
+              child1        |      |        |                |                  |       100% |
+              child2        |      |        |                |                  |        40% |
+              child3        |      |        |                |                  |       100% |          70%
+                grandchild1 |      |        |                |                  |        40% |
+                grandchild2 |      |        |                |                  |       100% |
+          TABLE
+          to: <<~TABLE
+            subject         | work | ∑ work | remaining work | ∑ remaining work | % complete | ∑ % complete
+            parent          |      |        |                |                  |        40% |
+              child1        |      |        |                |                  |       100% |
+              child2        |      |        |                |                  |        40% |
+              child3        |      |        |                |                  |       100% |
+                grandchild1 |      |        |                |                  |        40% |
+                grandchild2 |      |        |                |                  |       100% |
+          TABLE
+        )
+      end
+    end
+
+    context "on a multi-level hierarchy with work and remaining work values set" do
+      it "updates the total % complete of parent work packages" do
+        expect_performing_job_changes(
+          old_mode: "simple_average",
+          new_mode: "work_weighted_average",
+          from: <<~TABLE,
+            hierarchy       | work  | ∑ work | remaining work | ∑ remaining work | % complete | ∑ % complete
+            parent          |  10h  |    50h |             6h |              6h  |        40% |          63%
+              child1        |  15h  |        |             0h |                  |       100% |
+              child2        |       |        |                |                  |        40% |
+              child3        |   5h  |    25h |             0h |              0h  |       100% |          70%
+                grandchild1 |       |        |                |                  |        40% |
+                grandchild2 |   20h |        |             0h |                  |       100% |
+          TABLE
+          to: <<~TABLE
+            subject         | work  | ∑ work | remaining work | ∑ remaining work | % complete | ∑ % complete
+            parent          |  10h  |    50h |             6h |              6h  |        40% |          88%
+              child1        |  15h  |        |             0h |                  |       100% |
+              child2        |       |        |                |                  |        40% |
+              child3        |   5h  |    25h |             0h |              0h  |       100% |         100%
+                grandchild1 |       |        |                |                  |        40% |
+                grandchild2 |   20h |        |             0h |                  |       100% |
+          TABLE
+        )
+      end
+    end
+
+    describe "journal entries" do
+      it "is still not done" do
+        pending "TODO: Add specs for the journal entries created"
+        raise StandardError, "Not implemented"
+      end
+    end
+  end
+
+  context "with errors during job execution" do
+    let_work_packages(<<~TABLE)
+      subject     | work | ∑ work | remaining work | ∑ remaining work | % complete | ∑ % complete
+      wp          |  10h |    10h |             6h |               6h |        40% |          40%
+      wp 0%       |  10h |    10h |            10h |              10h |         0% |           0%
+      wp 40%      |  10h |    10h |             6h |               6h |        40% |          40%
+      wp 100%     |  10h |    10h |             0h |               0h |       100% |         100%
+    TABLE
+
+    before do
+      job.perform_now(cause_type: "should make it blow up!",
+                      old_mode: "simple_average",
+                      new_mode: "work_weighted_average")
+    rescue StandardError
+      # Catch the error to continue the test
+    end
+
+    it "does not update any work package" do
+      expect_work_packages(WorkPackage.all, <<~TABLE)
+        subject     | work | ∑ work | remaining work | ∑ remaining work | % complete | ∑ % complete
+        wp          |  10h |    10h |             6h |               6h |        40% |          40%
+        wp 0%       |  10h |    10h |            10h |              10h |         0% |           0%
+        wp 40%      |  10h |    10h |             6h |               6h |        40% |          40%
+        wp 100%     |  10h |    10h |             0h |               0h |       100% |         100%
+      TABLE
+    end
+
+    it "cleans up temporary database artifacts used throughout the job" do
+      expect(
+        ActiveRecord::Base.connection.table_exists?("temp_wp_progress_values")
+      ).to be(false)
+    end
+  end
+end