diff --git a/app/models/validations/sales/sale_information_validations.rb b/app/models/validations/sales/sale_information_validations.rb
index 54d49b7e0..17fbc95b4 100644
--- a/app/models/validations/sales/sale_information_validations.rb
+++ b/app/models/validations/sales/sale_information_validations.rb
@@ -64,4 +64,23 @@ module Validations::Sales::SaleInformationValidations
       record.errors.add :grant, I18n.t("validations.sale_information.grant.out_of_range")
     end
   end
+
+  def validate_stairbought(record)
+    return unless record.stairbought && record.type
+    return unless record.saledate && record.form.start_year_after_2024?
+
+    max_stairbought = case record.type
+                      when 30, 16, 28, 31, 32
+                        90
+                      when 2, 18
+                        75
+                      when 24
+                        50
+                      end
+
+    if max_stairbought && record.stairbought > max_stairbought
+      record.errors.add :stairbought, I18n.t("validations.sale_information.stairbought.over_max", max_stairbought:, type: record.form.get_question("type", record).answer_label(record))
+      record.errors.add :type, I18n.t("validations.sale_information.stairbought.over_max", max_stairbought:, type: record.form.get_question("type", record).answer_label(record))
+    end
+  end
 end
diff --git a/config/locales/en.yml b/config/locales/en.yml
index 7fc5f9d57..c7d8c9da2 100644
--- a/config/locales/en.yml
+++ b/config/locales/en.yml
@@ -617,6 +617,8 @@ en:
         higher_than_expected: "Basic monthly rent must be between £0.00 and £9,999.00"
       grant:
         out_of_range: "Loan, grants or subsidies must be between £9,000 and £16,000"
+      stairbought:
+        over_max: "The percentage bought in this staircasing transaction cannot be higher than %{max_stairbought}% for %{type} sales."
     merge_request:
       organisation_part_of_another_merge: "This organisation is part of another merge - select a different one"
       organisation_not_selected: "Select an organisation from the search list"
diff --git a/spec/models/validations/sales/sale_information_validations_spec.rb b/spec/models/validations/sales/sale_information_validations_spec.rb
index c890afed1..25474e55b 100644
--- a/spec/models/validations/sales/sale_information_validations_spec.rb
+++ b/spec/models/validations/sales/sale_information_validations_spec.rb
@@ -539,4 +539,73 @@ RSpec.describe Validations::Sales::SaleInformationValidations do
       end
     end
   end
+
+  describe "#validate_stairbought" do
+    let(:now) { Time.zone.local(2024, 4, 4) }
+
+    before do
+      Timecop.freeze(now)
+      Singleton.__init__(FormHandler)
+    end
+
+    after do
+      Timecop.return
+      Singleton.__init__(FormHandler)
+    end
+
+    [
+      ["Shared Ownership (new model lease)", 30, 90],
+      ["Home Ownership for people with Long-Term Disabilities (HOLD)", 16, 90],
+      ["Rent to Buy — Shared Ownership", 28, 90],
+      ["Right to Shared Ownership (RtSO)", 31, 90],
+      ["London Living Rent — Shared Ownership", 32, 90],
+      ["Shared Ownership (old model lease)", 2, 75],
+      ["Social HomeBuy — shared ownership purchase", 18, 75],
+      ["Older Persons Shared Ownership", 24, 50],
+    ].each do |label, type, max|
+      context "when ownership type is #{label}" do
+        let(:record) { build(:sales_log, ownershipsch: 1, type:, saledate: now) }
+
+        it "does not add an error if stairbought is under #{max}%" do
+          record.stairbought = max - 1
+          sale_information_validator.validate_stairbought(record)
+
+          expect(record.errors).to be_empty
+        end
+
+        it "does not add an error if stairbought is #{max}%" do
+          record.stairbought = max
+          sale_information_validator.validate_stairbought(record)
+
+          expect(record.errors).to be_empty
+        end
+
+        it "does not add an error if stairbought is not given" do
+          record.stairbought = nil
+          sale_information_validator.validate_stairbought(record)
+
+          expect(record.errors).to be_empty
+        end
+
+        it "adds an error if stairbought is over #{max}%" do
+          record.stairbought = max + 2
+          sale_information_validator.validate_stairbought(record)
+
+          expect(record.errors[:stairbought]).to include("The percentage bought in this staircasing transaction cannot be higher than #{max}% for #{label} sales.")
+          expect(record.errors[:type]).to include("The percentage bought in this staircasing transaction cannot be higher than #{max}% for #{label} sales.")
+        end
+      end
+    end
+
+    context "when the collection year is before 2024" do
+      let(:record) { build(:sales_log, ownershipsch: 1, type: 24, saledate: now, stairbought: 90) }
+      let(:now) { Time.zone.local(2023, 4, 4) }
+
+      it "does not add an error" do
+        sale_information_validator.validate_stairbought(record)
+
+        expect(record.errors).to be_empty
+      end
+    end
+  end
 end