diff --git a/app/models/derived_variables/lettings_log_variables.rb b/app/models/derived_variables/lettings_log_variables.rb
index d29f21ce2..960ecad52 100644
--- a/app/models/derived_variables/lettings_log_variables.rb
+++ b/app/models/derived_variables/lettings_log_variables.rb
@@ -128,6 +128,22 @@ private
         incref: 1,
       },
     },
+    {
+      conditions: {
+        net_income_known: 0,
+      },
+      derived_values: {
+        incref: 0,
+      },
+    },
+    {
+      conditions: {
+        net_income_known: 1,
+      },
+      derived_values: {
+        incref: 2,
+      },
+    },
   ].freeze
 
   def clear_inapplicable_derived_values!
diff --git a/lib/tasks/correct_incref_values.rake b/lib/tasks/correct_incref_values.rake
new file mode 100644
index 000000000..0b1921998
--- /dev/null
+++ b/lib/tasks/correct_incref_values.rake
@@ -0,0 +1,6 @@
+desc "Alter incref values for non imported lettings logs in the database"
+task correct_incref_values: :environment do
+  LettingsLog.where(old_id: nil, net_income_known: 0).update!(incref: 0)
+  LettingsLog.where(old_id: nil, net_income_known: 1).update!(incref: 2)
+  LettingsLog.where(old_id: nil, net_income_known: 2).update!(incref: 1)
+end
diff --git a/spec/lib/tasks/correct_incref_values_spec.rb b/spec/lib/tasks/correct_incref_values_spec.rb
new file mode 100644
index 000000000..fc046dcf6
--- /dev/null
+++ b/spec/lib/tasks/correct_incref_values_spec.rb
@@ -0,0 +1,36 @@
+require "rails_helper"
+require "rake"
+
+RSpec.describe "correct_incref_values" do
+  describe ":correct_incref_values", type: :task do
+    subject(:task) { Rake::Task["correct_incref_values"] }
+
+    before do
+      Rake.application.rake_require("tasks/correct_incref_values")
+      Rake::Task.define_task(:environment)
+      task.reenable
+    end
+
+    context "when the rake task is run" do
+      let!(:lettings_log) { create(:lettings_log, :completed) }
+
+      it "updates lettings logs with net_income_known 0 (yes) to have incref 0 (no)" do
+        lettings_log.update!(net_income_known: 0, incref: nil)
+        task.invoke
+        expect(lettings_log.reload.incref).to eq(0)
+      end
+
+      it "updates lettings logs with net_income_known 1 (no) to have incref 2 (don't know)" do
+        lettings_log.update!(net_income_known: 1, incref: nil)
+        task.invoke
+        expect(lettings_log.reload.incref).to eq(2)
+      end
+
+      it "updates lettings logs with net_income_known 2 (prefers not to say) to have incref 1 (yes)" do
+        lettings_log.update!(net_income_known: 2, incref: nil)
+        task.invoke
+        expect(lettings_log.reload.incref).to eq(1)
+      end
+    end
+  end
+end
diff --git a/spec/models/lettings_log_spec.rb b/spec/models/lettings_log_spec.rb
index b34377543..1ae394c3d 100644
--- a/spec/models/lettings_log_spec.rb
+++ b/spec/models/lettings_log_spec.rb
@@ -248,8 +248,13 @@ RSpec.describe LettingsLog do
     end
 
     it "correctly derives and saves incref" do
-      record_from_db = described_class.find(lettings_log.id)
-      expect(record_from_db["incref"]).to eq(1)
+      expect(lettings_log.reload.incref).to eq(1)
+
+      lettings_log.update!(net_income_known: 1)
+      expect(lettings_log.reload.incref).to eq(2)
+
+      lettings_log.update!(net_income_known: 0)
+      expect(lettings_log.reload.incref).to eq(0)
     end
 
     it "correctly derives and saves renttype" do