diff --git a/app/models/form/sales/pages/staircase_bought_value_check.rb b/app/models/form/sales/pages/staircase_bought_value_check.rb
new file mode 100644
index 000000000..b7b8178ff
--- /dev/null
+++ b/app/models/form/sales/pages/staircase_bought_value_check.rb
@@ -0,0 +1,27 @@
+class Form::Sales::Pages::StaircaseBoughtValueCheck < ::Form::Page
+  def initialize(id, hsh, subsection)
+    super
+    @id = "staircase_bought_value_check"
+    @depends_on = [
+      {
+        "staircase_bought_above_fifty?" => true,
+      },
+    ]
+    @title_text = {
+      "translation" => "soft_validations.staircase_bought_seems_high",
+      "arguments" => [
+        {
+          "key" => "stairbought",
+          "i18n_template" => "percentage",
+        },
+      ],
+    }
+    @informative_text = {}
+  end
+
+  def questions
+    @questions ||= [
+      Form::Sales::Questions::StaircaseBoughtValueCheck.new(nil, nil, self),
+    ]
+  end
+end
diff --git a/app/models/form/sales/questions/staircase_bought.rb b/app/models/form/sales/questions/staircase_bought.rb
index bdb5ac965..385cfb782 100644
--- a/app/models/form/sales/questions/staircase_bought.rb
+++ b/app/models/form/sales/questions/staircase_bought.rb
@@ -8,6 +8,6 @@ class Form::Sales::Questions::StaircaseBought < ::Form::Question
     @width = 5
     @min = 0
     @max = 100
-    @suffix = " percent"
+    @suffix = "%"
   end
 end
diff --git a/app/models/form/sales/questions/staircase_bought_value_check.rb b/app/models/form/sales/questions/staircase_bought_value_check.rb
new file mode 100644
index 000000000..65fe02e66
--- /dev/null
+++ b/app/models/form/sales/questions/staircase_bought_value_check.rb
@@ -0,0 +1,23 @@
+class Form::Sales::Questions::StaircaseBoughtValueCheck < ::Form::Question
+  def initialize(id, hsh, page)
+    super
+    @id = "staircase_bought_value_check"
+    @check_answer_label = "Percentage bought confirmation"
+    @header = "Are you sure this is correct?"
+    @type = "interruption_screen"
+    @answer_options = {
+      "0" => { "value" => "Yes" },
+      "1" => { "value" => "No" },
+    }
+    @hidden_in_check_answers = {
+      "depends_on" => [
+        {
+          "staircase_bought_value_check" => 0,
+        },
+        {
+          "staircase_bought_value_check" => 1,
+        },
+      ],
+    }
+  end
+end
diff --git a/app/models/form/sales/questions/staircase_owned.rb b/app/models/form/sales/questions/staircase_owned.rb
index 6f9e13b14..7e6dab5d6 100644
--- a/app/models/form/sales/questions/staircase_owned.rb
+++ b/app/models/form/sales/questions/staircase_owned.rb
@@ -8,6 +8,6 @@ class Form::Sales::Questions::StaircaseOwned < ::Form::Question
     @width = 5
     @min = 0
     @max = 100
-    @suffix = " percent"
+    @suffix = "%"
   end
 end
diff --git a/app/models/form/sales/subsections/shared_ownership_scheme.rb b/app/models/form/sales/subsections/shared_ownership_scheme.rb
index e7ff1cf6e..0e2e3fdda 100644
--- a/app/models/form/sales/subsections/shared_ownership_scheme.rb
+++ b/app/models/form/sales/subsections/shared_ownership_scheme.rb
@@ -11,6 +11,7 @@ class Form::Sales::Subsections::SharedOwnershipScheme < ::Form::Subsection
       Form::Sales::Pages::LivingBeforePurchase.new("living_before_purchase_shared_ownership", nil, self),
       Form::Sales::Pages::Staircase.new(nil, nil, self),
       Form::Sales::Pages::AboutStaircase.new(nil, nil, self),
+      Form::Sales::Pages::StaircaseBoughtValueCheck.new(nil, nil, self),
       Form::Sales::Pages::Resale.new(nil, nil, self),
       Form::Sales::Pages::ExchangeDate.new(nil, nil, self),
       Form::Sales::Pages::HandoverDate.new(nil, nil, self),
diff --git a/app/models/validations/sales/financial_validations.rb b/app/models/validations/sales/financial_validations.rb
index 233f32b6b..df7dc8df5 100644
--- a/app/models/validations/sales/financial_validations.rb
+++ b/app/models/validations/sales/financial_validations.rb
@@ -27,4 +27,21 @@ module Validations::Sales::FinancialValidations
       record.errors.add :cashdis, I18n.t("validations.financial.cash_discount_invalid")
     end
   end
+
+  def validate_percentage_bought_not_greater_than_percentage_owned(record)
+    return unless record.stairbought && record.stairowned
+
+    if record.stairbought > record.stairowned
+      record.errors.add :stairowned, I18n.t("validations.financial.staircasing.percentage_bought_must_be_greater_than_percentage_owned")
+    end
+  end
+
+  def validate_percentage_owned_not_too_much_if_older_person(record)
+    return unless record.old_persons_shared_ownership? && record.stairowned
+
+    if record.stairowned > 75
+      record.errors.add :stairowned, I18n.t("validations.financial.staircasing.older_person_percentage_owned_maximum_75")
+      record.errors.add :type, I18n.t("validations.financial.staircasing.older_person_percentage_owned_maximum_75")
+    end
+  end
 end
diff --git a/app/models/validations/sales/soft_validations.rb b/app/models/validations/sales/soft_validations.rb
index 70af22fec..0bffe1234 100644
--- a/app/models/validations/sales/soft_validations.rb
+++ b/app/models/validations/sales/soft_validations.rb
@@ -13,6 +13,10 @@ module Validations::Sales::SoftValidations
     income1 < ALLOWED_INCOME_RANGES[ecstat1][:soft_min]
   end
 
+  def staircase_bought_above_fifty?
+    stairbought && stairbought > 50
+  end
+
   def mortgage_over_soft_max?
     return false unless mortgage && inc1mort && inc2mort
     return false if income1_used_for_mortgage? && income1.blank? || income2_used_for_mortgage? && income2.blank?
diff --git a/config/locales/en.yml b/config/locales/en.yml
index 1ec13a304..98f57ae73 100644
--- a/config/locales/en.yml
+++ b/config/locales/en.yml
@@ -277,6 +277,10 @@ en:
         out_of_range: "Household rent and other charges must be between %{min_chcharge} and %{max_chcharge} if paying %{period}"
         not_provided: "Enter how much rent and other charges the household pays %{period}"
       cash_discount_invalid: "Cash discount must be £0 - £999,999"
+      staircasing:
+        percentage_bought_must_be_greater_than_percentage_owned: "Total percentage buyer now owns must be more than percentage bought in this transaction"
+        older_person_percentage_owned_maximum_75: "Percentage cannot be above 75% under Older Person's Shared Ownership"
+
     household:
       reasonpref:
         not_homeless: "Answer cannot be ‘homeless or about to lose their home’ as the tenant was not homeless immediately prior to this letting"
diff --git a/db/migrate/20230125152916_add_staircase_bought_value_check_to_sales_log.rb b/db/migrate/20230125152916_add_staircase_bought_value_check_to_sales_log.rb
new file mode 100644
index 000000000..d7e227afa
--- /dev/null
+++ b/db/migrate/20230125152916_add_staircase_bought_value_check_to_sales_log.rb
@@ -0,0 +1,5 @@
+class AddStaircaseBoughtValueCheckToSalesLog < ActiveRecord::Migration[7.0]
+  def change
+    add_column :sales_logs, :staircase_bought_value_check, :integer
+  end
+end
diff --git a/db/schema.rb b/db/schema.rb
index 940e172fd..dc431d425 100644
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -504,9 +504,10 @@ ActiveRecord::Schema[7.0].define(version: 2023_01_26_145529) do
     t.integer "retirement_value_check"
     t.integer "hodate_check"
     t.integer "extrabor_value_check"
+    t.integer "grant_value_check"
+    t.integer "staircase_bought_value_check"
     t.integer "deposit_and_mortgage_value_check"
     t.integer "shared_ownership_deposit_value_check"
-    t.integer "grant_value_check"
     t.integer "old_persons_shared_ownership_value_check"
     t.index ["bulk_upload_id"], name: "index_sales_logs_on_bulk_upload_id"
     t.index ["created_by_id"], name: "index_sales_logs_on_created_by_id"
diff --git a/spec/models/form/sales/questions/staircase_bought_spec.rb b/spec/models/form/sales/questions/staircase_bought_spec.rb
index 96716dbd3..7b877cc26 100644
--- a/spec/models/form/sales/questions/staircase_bought_spec.rb
+++ b/spec/models/form/sales/questions/staircase_bought_spec.rb
@@ -44,7 +44,7 @@ RSpec.describe Form::Sales::Questions::StaircaseBought, type: :model do
   end
 
   it "has correct suffix" do
-    expect(question.suffix).to eq(" percent")
+    expect(question.suffix).to eq("%")
   end
 
   it "has correct min" do
diff --git a/spec/models/form/sales/questions/staircase_owned_spec.rb b/spec/models/form/sales/questions/staircase_owned_spec.rb
index 56b563990..cbd577784 100644
--- a/spec/models/form/sales/questions/staircase_owned_spec.rb
+++ b/spec/models/form/sales/questions/staircase_owned_spec.rb
@@ -44,7 +44,7 @@ RSpec.describe Form::Sales::Questions::StaircaseOwned, type: :model do
   end
 
   it "has correct suffix" do
-    expect(question.suffix).to eq(" percent")
+    expect(question.suffix).to eq("%")
   end
 
   it "has correct min" do
diff --git a/spec/models/form/sales/subsections/shared_ownership_scheme_spec.rb b/spec/models/form/sales/subsections/shared_ownership_scheme_spec.rb
index d131bc605..58a762ccb 100644
--- a/spec/models/form/sales/subsections/shared_ownership_scheme_spec.rb
+++ b/spec/models/form/sales/subsections/shared_ownership_scheme_spec.rb
@@ -17,6 +17,7 @@ RSpec.describe Form::Sales::Subsections::SharedOwnershipScheme, type: :model do
         living_before_purchase_shared_ownership
         staircasing
         about_staircasing
+        staircase_bought_value_check
         resale
         exchange_contracts
         handover_date
diff --git a/spec/models/form_handler_spec.rb b/spec/models/form_handler_spec.rb
index 89f550bee..be88b2b94 100644
--- a/spec/models/form_handler_spec.rb
+++ b/spec/models/form_handler_spec.rb
@@ -52,14 +52,14 @@ RSpec.describe FormHandler do
     it "is able to load a current sales form" do
       form = form_handler.get_form("current_sales")
       expect(form).to be_a(Form)
-      expect(form.pages.count).to eq(197)
+      expect(form.pages.count).to eq(198)
       expect(form.name).to eq("2022_2023_sales")
     end
 
     it "is able to load a previous sales form" do
       form = form_handler.get_form("previous_sales")
       expect(form).to be_a(Form)
-      expect(form.pages.count).to eq(197)
+      expect(form.pages.count).to eq(198)
       expect(form.name).to eq("2021_2022_sales")
     end
   end
diff --git a/spec/models/validations/sales/financial_validations_spec.rb b/spec/models/validations/sales/financial_validations_spec.rb
index 4bc19afbe..88f36943f 100644
--- a/spec/models/validations/sales/financial_validations_spec.rb
+++ b/spec/models/validations/sales/financial_validations_spec.rb
@@ -99,4 +99,63 @@ RSpec.describe Validations::Sales::FinancialValidations do
       expect(record.errors["cashdis"]).to be_empty
     end
   end
+
+  describe "#validate_percentage_bought_not_greater_than_percentage_owned" do
+    let(:record) { FactoryBot.create(:sales_log) }
+
+    it "does not add an error if the percentage bought is less than the percentage owned" do
+      record.stairbought = 20
+      record.stairowned = 40
+      financial_validator.validate_percentage_bought_not_greater_than_percentage_owned(record)
+      expect(record.errors["stairbought"]).to be_empty
+      expect(record.errors["stairowned"]).to be_empty
+    end
+
+    it "does not add an error if the percentage bought is equal to the percentage owned" do
+      record.stairbought = 30
+      record.stairowned = 30
+      financial_validator.validate_percentage_bought_not_greater_than_percentage_owned(record)
+      expect(record.errors["stairbought"]).to be_empty
+      expect(record.errors["stairowned"]).to be_empty
+    end
+
+    it "adds an error to stairowned and not stairbought if the percentage bought is more than the percentage owned" do
+      record.stairbought = 50
+      record.stairowned = 40
+      financial_validator.validate_percentage_bought_not_greater_than_percentage_owned(record)
+      expect(record.errors["stairowned"]).to include(match I18n.t("validations.financial.staircasing.percentage_bought_must_be_greater_than_percentage_owned"))
+    end
+  end
+
+  describe "#validate_percentage_owned_not_too_much_if_older_person" do
+    let(:record) { FactoryBot.create(:sales_log) }
+
+    context "when log type is not older persons shared ownership" do
+      it "does not add an error when percentage owned after staircasing transaction exceeds 75%" do
+        record.type = 2
+        record.stairowned = 80
+        financial_validator.validate_percentage_owned_not_too_much_if_older_person(record)
+        expect(record.errors["stairowned"]).to be_empty
+        expect(record.errors["type"]).to be_empty
+      end
+    end
+
+    context "when log type is older persons shared ownership" do
+      it "does not add an error when percentage owned after staircasing transaction is less than 75%" do
+        record.type = 24
+        record.stairowned = 50
+        financial_validator.validate_percentage_owned_not_too_much_if_older_person(record)
+        expect(record.errors["stairowned"]).to be_empty
+        expect(record.errors["type"]).to be_empty
+      end
+
+      it "adds an error when percentage owned after staircasing transaction exceeds 75%" do
+        record.type = 24
+        record.stairowned = 90
+        financial_validator.validate_percentage_owned_not_too_much_if_older_person(record)
+        expect(record.errors["stairowned"]).to include(match I18n.t("validations.financial.staircasing.older_person_percentage_owned_maximum_75"))
+        expect(record.errors["type"]).to include(match I18n.t("validations.financial.staircasing.older_person_percentage_owned_maximum_75"))
+      end
+    end
+  end
 end
diff --git a/spec/models/validations/sales/soft_validations_spec.rb b/spec/models/validations/sales/soft_validations_spec.rb
index 234f810bc..dc873bc97 100644
--- a/spec/models/validations/sales/soft_validations_spec.rb
+++ b/spec/models/validations/sales/soft_validations_spec.rb
@@ -367,7 +367,7 @@ RSpec.describe Validations::Sales::SoftValidations do
           .to be_deposit_over_soft_max
       end
 
-      it "returns fals if deposit is less than 4/3 of savings" do
+      it "returns false if deposit is less than 4/3 of savings" do
         record.deposit = 7_999
         record.savings = 6_000
         expect(record)
@@ -573,4 +573,24 @@ RSpec.describe Validations::Sales::SoftValidations do
       expect(record).not_to be_grant_outside_common_range
     end
   end
+
+  describe "#staircase_bought_above_fifty" do
+    it "returns false when stairbought is not set" do
+      record.stairbought = nil
+
+      expect(record).not_to be_staircase_bought_above_fifty
+    end
+
+    it "returns false when stairbought is below fifty" do
+      record.stairbought = 40
+
+      expect(record).not_to be_staircase_bought_above_fifty
+    end
+
+    it "returns true when stairbought is above fifty" do
+      record.stairbought = 70
+
+      expect(record).to be_staircase_bought_above_fifty
+    end
+  end
 end
diff --git a/spec/models/validations/shared_validations_spec.rb b/spec/models/validations/shared_validations_spec.rb
index abdde5f45..c1d8cb3af 100644
--- a/spec/models/validations/shared_validations_spec.rb
+++ b/spec/models/validations/shared_validations_spec.rb
@@ -70,11 +70,11 @@ RSpec.describe Validations::SharedValidations do
     end
 
     context "when validating percent" do
-      it "validates that % suffix is added in the error message" do
-        sales_record.stairbought = "random"
+      it "validates that suffixes are added in the error message" do
+        sales_record.stairbought = 150
         shared_validator.validate_numeric_min_max(sales_record)
         expect(sales_record.errors["stairbought"])
-          .to include(match I18n.t("validations.numeric.valid", field: "Percentage bought in this staircasing transaction", min: "0 percent", max: "100 percent"))
+          .to include(match I18n.t("validations.numeric.valid", field: "Percentage bought in this staircasing transaction", min: "0%", max: "100%"))
       end
     end