diff --git a/app/models/case_log.rb b/app/models/case_log.rb
index 50444d311..30a16a21e 100644
--- a/app/models/case_log.rb
+++ b/app/models/case_log.rb
@@ -56,6 +56,20 @@ class CaseLog < ApplicationRecord
   enum ecstat6: ECSTAT, _suffix: true
   enum ecstat7: ECSTAT, _suffix: true
   enum ecstat8: ECSTAT, _suffix: true
+  enum relat2: RELAT, _suffix: true
+  enum relat3: RELAT, _suffix: true
+  enum relat4: RELAT, _suffix: true
+  enum relat5: RELAT, _suffix: true
+  enum relat6: RELAT, _suffix: true
+  enum relat7: RELAT, _suffix: true
+  enum relat8: RELAT, _suffix: true
+  enum sex2: GENDER, _suffix: true
+  enum sex3: GENDER, _suffix: true
+  enum sex4: GENDER, _suffix: true
+  enum sex5: GENDER, _suffix: true
+  enum sex6: GENDER, _suffix: true
+  enum sex7: GENDER, _suffix: true
+  enum sex8: GENDER, _suffix: true
   enum prevten: PREVIOUS_TENANCY, _suffix: true
   enum homeless: HOMELESS, _suffix: true
   enum underoccupation_benefitcap: BENEFITCAP, _suffix: true
@@ -119,7 +133,7 @@ class CaseLog < ApplicationRecord
   enum postcode_known: POLAR, _suffix: true
   enum la_known: POLAR, _suffix: true
 
-  AUTOGENERATED_FIELDS = %w[id status created_at updated_at discarded_at renttype lettype is_la_inferred].freeze
+  AUTOGENERATED_FIELDS = %w[id status created_at updated_at discarded_at renttype lettype is_la_inferred totchild].freeze
   OPTIONAL_FIELDS = %w[postcode_known
                        la_known
                        first_time_property_let_as_social_housing].freeze
@@ -199,6 +213,12 @@ private
     self.lettype = "#{renttype} #{needstype} #{owning_organisation['Org type']}" if renttype.present? && needstype.present? && owning_organisation["Org type"].present?
     self.is_la_inferred = false if is_la_inferred.nil?
     self.la = get_la(property_postcode)
+    self.totchild = get_totchild
+  end
+
+  def get_totchild
+    relationships = [relat2, relat3, relat4, relat5, relat6, relat7, relat8]
+    relationships.count("Child - includes young adult and grown-up")
   end
 
   def get_la(postcode)
diff --git a/app/models/constants/case_log.rb b/app/models/constants/case_log.rb
index 3a537035d..a7a5322a0 100644
--- a/app/models/constants/case_log.rb
+++ b/app/models/constants/case_log.rb
@@ -733,4 +733,18 @@ module Constants::CaseLog
                      "Waltham Forest",
                      "Wandsworth",
                      "Westminster"].freeze
+
+  RELAT = {
+    "Child - includes young adult and grown-up" => "C",
+    "Partner" => "P",
+    "Other" => "X",
+    "Prefer not to say" => "R",
+  }.freeze
+
+  GENDER = {
+    "Female" => "F",
+    "Male" => "M",
+    "Non-binary" => "X",
+    "Prefer not to say" => "R",
+  }.freeze
 end
diff --git a/db/migrate/20211214143841_add_totchild.rb b/db/migrate/20211214143841_add_totchild.rb
new file mode 100644
index 000000000..e4fe045e5
--- /dev/null
+++ b/db/migrate/20211214143841_add_totchild.rb
@@ -0,0 +1,7 @@
+class AddTotchild < ActiveRecord::Migration[6.1]
+  def change
+    change_table :case_logs, bulk: true do |t|
+      t.column :totchild, :integer
+    end
+  end
+end
diff --git a/db/schema.rb b/db/schema.rb
index 70cdb5569..dce7cd20a 100644
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 2021_12_13_122642) do
+ActiveRecord::Schema.define(version: 2021_12_14_143841) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -175,6 +175,7 @@ ActiveRecord::Schema.define(version: 2021_12_13_122642) do
     t.integer "month"
     t.integer "year"
     t.boolean "is_la_inferred"
+    t.integer "totchild"
     t.index ["discarded_at"], name: "index_case_logs_on_discarded_at"
     t.index ["managing_organisation_id"], name: "index_case_logs_on_managing_organisation_id"
     t.index ["owning_organisation_id"], name: "index_case_logs_on_owning_organisation_id"
diff --git a/spec/models/case_log_spec.rb b/spec/models/case_log_spec.rb
index c8ad9195e..ea4e353f7 100644
--- a/spec/models/case_log_spec.rb
+++ b/spec/models/case_log_spec.rb
@@ -1059,5 +1059,26 @@ RSpec.describe Form, type: :model do
         expect(record_from_db["la"]).to eq(nil)
       end
     end
+
+    context "household members derived vars" do
+      let!(:household_case_log) do
+        CaseLog.create({
+          managing_organisation: organisation,
+          owning_organisation: organisation,
+          other_hhmemb: 4,
+          relat2: "Child - includes young adult and grown-up",
+          relat3: "Child - includes young adult and grown-up",
+          relat4: "Other",
+          relat5: "Child - includes young adult and grown-up",
+        })
+      end
+
+      it "correctly derives and saves totchild" do
+        household_case_log.reload
+
+        record_from_db = ActiveRecord::Base.connection.execute("select totchild from case_logs where id=#{household_case_log.id}").to_a[0]
+        expect(record_from_db["totchild"]).to eq(3)
+      end
+    end
   end
 end