diff --git a/app/models/form/sales/pages/about_deposit_with_discount.rb b/app/models/form/sales/pages/about_deposit_with_discount.rb
index 1c684b0bc..5d1e41a95 100644
--- a/app/models/form/sales/pages/about_deposit_with_discount.rb
+++ b/app/models/form/sales/pages/about_deposit_with_discount.rb
@@ -1,15 +1,22 @@
 class Form::Sales::Pages::AboutDepositWithDiscount < ::Form::Page
-  def initialize(id, hsh, subsection)
-    super
-    @id = "about_deposit_with_discount"
+  def initialize(id, hsh, subsection, optional:)
+    super(id, hsh, subsection)
     @header = "About the deposit"
-    @depends_on = [{ "is_type_discount?" => true }]
+    @optional = optional
   end
 
   def questions
     @questions ||= [
-      Form::Sales::Questions::DepositAmount.new(nil, nil, self, ownershipsch: 1),
+      Form::Sales::Questions::DepositAmount.new(nil, nil, self, ownershipsch: 1, optional: @optional),
       Form::Sales::Questions::DepositDiscount.new(nil, nil, self),
     ]
   end
+
+  def depends_on
+    if form.start_year_after_2024?
+      [{ "is_type_discount?" => true, "stairowned_100?" => @optional }]
+    else
+      [{ "is_type_discount?" => true }]
+    end
+  end
 end
diff --git a/app/models/form/sales/pages/about_deposit_without_discount.rb b/app/models/form/sales/pages/about_deposit_without_discount.rb
index 1114b8f84..fdd74cf31 100644
--- a/app/models/form/sales/pages/about_deposit_without_discount.rb
+++ b/app/models/form/sales/pages/about_deposit_without_discount.rb
@@ -1,16 +1,26 @@
 class Form::Sales::Pages::AboutDepositWithoutDiscount < ::Form::Page
-  def initialize(id, hsh, subsection, ownershipsch:)
+  def initialize(id, hsh, subsection, ownershipsch:, optional:)
     super(id, hsh, subsection)
     @header = "About the deposit"
-    @depends_on = [{ "is_type_discount?" => false, "ownershipsch" => 1 },
-                   { "ownershipsch" => 2 },
-                   { "ownershipsch" => 3, "mortgageused" => 1 }]
     @ownershipsch = ownershipsch
+    @optional = optional
   end
 
   def questions
     @questions ||= [
-      Form::Sales::Questions::DepositAmount.new(nil, nil, self, ownershipsch: @ownershipsch),
+      Form::Sales::Questions::DepositAmount.new(nil, nil, self, ownershipsch: @ownershipsch, optional: @optional),
     ]
   end
+
+  def depends_on
+    if form.start_year_after_2024?
+      [{ "is_type_discount?" => false, "ownershipsch" => 1, "stairowned_100?" => @optional },
+       { "ownershipsch" => 2 },
+       { "ownershipsch" => 3, "mortgageused" => 1 }]
+    else
+      [{ "is_type_discount?" => false, "ownershipsch" => 1 },
+       { "ownershipsch" => 2 },
+       { "ownershipsch" => 3, "mortgageused" => 1 }]
+    end
+  end
 end
diff --git a/app/models/form/sales/questions/deposit_amount.rb b/app/models/form/sales/questions/deposit_amount.rb
index 784bb56a1..689299e56 100644
--- a/app/models/form/sales/questions/deposit_amount.rb
+++ b/app/models/form/sales/questions/deposit_amount.rb
@@ -1,5 +1,5 @@
 class Form::Sales::Questions::DepositAmount < ::Form::Question
-  def initialize(id, hsh, subsection, ownershipsch:)
+  def initialize(id, hsh, subsection, ownershipsch:, optional:)
     super(id, hsh, subsection)
     @id = "deposit"
     @check_answer_label = "Cash deposit"
@@ -10,10 +10,10 @@ class Form::Sales::Questions::DepositAmount < ::Form::Question
     @step = 1
     @width = 5
     @prefix = "£"
-    @hint_text = "Enter the total cash sum paid by the buyer towards the property that was not funded by the mortgage"
     @derived = true
     @ownershipsch = ownershipsch
     @question_number = question_number
+    @optional = optional
   end
 
   def selected_answer_option_is_derived?(_log)
@@ -30,4 +30,12 @@ class Form::Sales::Questions::DepositAmount < ::Form::Question
       116
     end
   end
+
+  def hint_text
+    if @optional
+      "Enter the total cash sum paid by the buyer towards the property that was not funded by the mortgage. As this is a fully staircased sale this question is optional. If you do not have the information available click save and continue"
+    else
+      "Enter the total cash sum paid by the buyer towards the property that was not funded by the mortgage"
+    end
+  end
 end
diff --git a/app/models/form/sales/subsections/discounted_ownership_scheme.rb b/app/models/form/sales/subsections/discounted_ownership_scheme.rb
index 52ee9e95c..200565ab6 100644
--- a/app/models/form/sales/subsections/discounted_ownership_scheme.rb
+++ b/app/models/form/sales/subsections/discounted_ownership_scheme.rb
@@ -31,7 +31,7 @@ class Form::Sales::Subsections::DiscountedOwnershipScheme < ::Form::Subsection
       Form::Sales::Pages::MortgageLength.new("mortgage_length_discounted_ownership", nil, self, ownershipsch: 2),
       Form::Sales::Pages::ExtraBorrowing.new("extra_borrowing_discounted_ownership", nil, self, ownershipsch: 2),
       Form::Sales::Pages::ExtraBorrowingValueCheck.new("extra_borrowing_value_check", nil, self),
-      Form::Sales::Pages::AboutDepositWithoutDiscount.new("about_deposit_discounted_ownership", nil, self, ownershipsch: 2),
+      Form::Sales::Pages::AboutDepositWithoutDiscount.new("about_deposit_discounted_ownership", nil, self, ownershipsch: 2, optional: false),
       Form::Sales::Pages::ExtraBorrowingValueCheck.new("extra_borrowing_deposit_value_check", nil, self),
       Form::Sales::Pages::DepositValueCheck.new("discounted_ownership_deposit_value_check", nil, self),
       Form::Sales::Pages::DepositAndMortgageValueCheck.new("discounted_ownership_deposit_and_mortgage_value_check_after_deposit", nil, self),
diff --git a/app/models/form/sales/subsections/outright_sale.rb b/app/models/form/sales/subsections/outright_sale.rb
index 245cbcb10..39275d7b2 100644
--- a/app/models/form/sales/subsections/outright_sale.rb
+++ b/app/models/form/sales/subsections/outright_sale.rb
@@ -18,7 +18,7 @@ class Form::Sales::Subsections::OutrightSale < ::Form::Subsection
       (Form::Sales::Pages::MortgageLenderOther.new("mortgage_lender_other_outright_sale", nil, self, ownershipsch: 3) unless form.start_year_after_2024?),
       Form::Sales::Pages::MortgageLength.new("mortgage_length_outright_sale", nil, self, ownershipsch: 3),
       Form::Sales::Pages::ExtraBorrowing.new("extra_borrowing_outright_sale", nil, self, ownershipsch: 3),
-      Form::Sales::Pages::AboutDepositWithoutDiscount.new("about_deposit_outright_sale", nil, self, ownershipsch: 3),
+      Form::Sales::Pages::AboutDepositWithoutDiscount.new("about_deposit_outright_sale", nil, self, ownershipsch: 3, optional: false),
       Form::Sales::Pages::DepositValueCheck.new("outright_sale_deposit_value_check", nil, self),
       leasehold_charge_pages,
       Form::Sales::Pages::MonthlyChargesValueCheck.new("monthly_charges_outright_sale_value_check", nil, self),
diff --git a/app/models/form/sales/subsections/shared_ownership_scheme.rb b/app/models/form/sales/subsections/shared_ownership_scheme.rb
index 66a711dcd..51abe3656 100644
--- a/app/models/form/sales/subsections/shared_ownership_scheme.rb
+++ b/app/models/form/sales/subsections/shared_ownership_scheme.rb
@@ -37,14 +37,16 @@ class Form::Sales::Subsections::SharedOwnershipScheme < ::Form::Subsection
       Form::Sales::Pages::MortgageLenderOther.new("mortgage_lender_other_shared_ownership", nil, self, ownershipsch: 1),
       Form::Sales::Pages::MortgageLength.new("mortgage_length_shared_ownership", nil, self, ownershipsch: 1),
       Form::Sales::Pages::ExtraBorrowing.new("extra_borrowing_shared_ownership", nil, self, ownershipsch: 1),
-      Form::Sales::Pages::AboutDepositWithDiscount.new(nil, nil, self),
-      Form::Sales::Pages::AboutDepositWithoutDiscount.new("about_deposit_shared_ownership", nil, self, ownershipsch: 1),
+      Form::Sales::Pages::AboutDepositWithDiscount.new("about_deposit_with_discount", nil, self, optional: false),
+      (Form::Sales::Pages::AboutDepositWithDiscount.new("about_deposit_with_discount_optional", nil, self, optional: true) if form.start_year_after_2024?),
+      Form::Sales::Pages::AboutDepositWithoutDiscount.new("about_deposit_shared_ownership", nil, self, ownershipsch: 1, optional: false),
+      (Form::Sales::Pages::AboutDepositWithoutDiscount.new("about_deposit_shared_ownership_optional", nil, self, ownershipsch: 1, optional: true) if form.start_year_after_2024?),
       Form::Sales::Pages::DepositValueCheck.new("deposit_value_check", nil, self),
       Form::Sales::Pages::SharedOwnershipDepositValueCheck.new("shared_ownership_deposit_value_check", nil, self),
       Form::Sales::Pages::MonthlyRent.new(nil, nil, self),
       Form::Sales::Pages::LeaseholdCharges.new("leasehold_charges_shared_ownership", nil, self, ownershipsch: 1),
       Form::Sales::Pages::MonthlyChargesValueCheck.new("monthly_charges_shared_ownership_value_check", nil, self),
-    ]
+    ].compact
   end
 
   def displayed_in_tasklist?(log)
diff --git a/app/models/sales_log.rb b/app/models/sales_log.rb
index 76c43b09e..13d16a786 100644
--- a/app/models/sales_log.rb
+++ b/app/models/sales_log.rb
@@ -121,6 +121,7 @@ class SalesLog < Log
     not_required << "proplen" if proplen_optional?
     not_required << "mortlen" if mortlen_optional?
     not_required << "frombeds" if frombeds_optional?
+    not_required << "deposit" if form.start_year_after_2024? && stairowned_100?
 
     not_required |= %w[address_line2 county postcode_full] if saledate && collection_start_year_for_date(saledate) >= 2023
 
@@ -495,4 +496,8 @@ class SalesLog < Log
   def is_not_staircasing?
     staircase == 2 || staircase == 3
   end
+
+  def stairowned_100?
+    stairowned == 100
+  end
 end
diff --git a/app/models/validations/sales/sale_information_validations.rb b/app/models/validations/sales/sale_information_validations.rb
index 0aaa77a93..c8a4e46dc 100644
--- a/app/models/validations/sales/sale_information_validations.rb
+++ b/app/models/validations/sales/sale_information_validations.rb
@@ -110,4 +110,14 @@ module Validations::Sales::SaleInformationValidations
       end
     end
   end
+
+  def validate_mortgage_used_and_stairbought(record)
+    return unless record.stairowned && record.mortgageused
+    return unless record.saledate && record.form.start_year_after_2024?
+
+    if !record.stairowned_100? && record.mortgageused == 3
+      record.errors.add :stairowned, I18n.t("validations.sale_information.stairowned.mortgageused_dont_know")
+      record.errors.add :mortgageused, I18n.t("validations.sale_information.stairowned.mortgageused_dont_know")
+    end
+  end
 end
diff --git a/app/services/bulk_upload/sales/year2024/row_parser.rb b/app/services/bulk_upload/sales/year2024/row_parser.rb
index 28e7ef100..c7a5349d0 100644
--- a/app/services/bulk_upload/sales/year2024/row_parser.rb
+++ b/app/services/bulk_upload/sales/year2024/row_parser.rb
@@ -341,6 +341,14 @@ class BulkUpload::Sales::Year2024::RowParser
             },
             on: :before_log
 
+  validates :field_103,
+            inclusion: {
+              in: [1, 2],
+              if: proc { field_88 != 100 },
+              question: QUESTIONS[:field_103],
+            },
+            on: :before_log
+
   validates :field_9,
             presence: {
               message: I18n.t("validations.not_answered", question: "type of shared ownership sale"),
diff --git a/config/locales/en.yml b/config/locales/en.yml
index 204a20b4e..37239d234 100644
--- a/config/locales/en.yml
+++ b/config/locales/en.yml
@@ -623,6 +623,8 @@ en:
         over_discounted_london_max: "The percentage discount multiplied by the purchase price is %{discount_value}. This figure should not be more than £136,400 for properties in London."
         over_discounted_max: "The percentage discount multiplied by the purchase price is %{discount_value}. This figure should not be more than £102,400 for properties outside of London."
       non_staircasing_mortgage: "The mortgage and deposit added together is %{mortgage_and_deposit_total} and the purchase price times by the equity is %{expected_shared_ownership_deposit_value}. These figures should be the same."
+      stairowned:
+        mortgageused_dont_know: "The percentage owned has to be 100% if the mortgage used is 'Don’t know'"
     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/form/sales/pages/about_deposit_with_discount_spec.rb b/spec/models/form/sales/pages/about_deposit_with_discount_spec.rb
index cc33a9641..89db397f1 100644
--- a/spec/models/form/sales/pages/about_deposit_with_discount_spec.rb
+++ b/spec/models/form/sales/pages/about_deposit_with_discount_spec.rb
@@ -1,12 +1,16 @@
 require "rails_helper"
 
 RSpec.describe Form::Sales::Pages::AboutDepositWithDiscount, type: :model do
-  subject(:page) { described_class.new(page_id, page_definition, subsection) }
+  subject(:page) { described_class.new(page_id, page_definition, subsection, optional: false) }
 
-  let(:page_id) { nil }
+  let(:page_id) { "about_deposit_with_discount" }
   let(:page_definition) { nil }
   let(:subsection) { instance_double(Form::Subsection) }
 
+  before do
+    allow(subsection).to receive(:form).and_return(instance_double(Form, start_year_after_2024?: false))
+  end
+
   it "has correct subsection" do
     expect(page.subsection).to eq(subsection)
   end
@@ -32,4 +36,36 @@ RSpec.describe Form::Sales::Pages::AboutDepositWithDiscount, type: :model do
       [{ "is_type_discount?" => true }],
     )
   end
+
+  context "when optional" do
+    subject(:page) { described_class.new(page_id, page_definition, subsection, optional: true) }
+
+    it "has correct depends_on" do
+      expect(page.depends_on).to eq(
+        [{ "is_type_discount?" => true }],
+      )
+    end
+  end
+
+  context "when it's a 2024 form" do
+    before do
+      allow(subsection).to receive(:form).and_return(instance_double(Form, start_year_after_2024?: true))
+    end
+
+    it "has correct depends_on" do
+      expect(page.depends_on).to eq(
+        [{ "is_type_discount?" => true, "stairowned_100?" => false }],
+      )
+    end
+
+    context "and optional" do
+      subject(:page) { described_class.new(page_id, page_definition, subsection, optional: true) }
+
+      it "has correct depends_on" do
+        expect(page.depends_on).to eq(
+          [{ "is_type_discount?" => true, "stairowned_100?" => true }],
+        )
+      end
+    end
+  end
 end
diff --git a/spec/models/form/sales/pages/about_deposit_without_discount_spec.rb b/spec/models/form/sales/pages/about_deposit_without_discount_spec.rb
index 1a0b5ef4d..1a4e420c6 100644
--- a/spec/models/form/sales/pages/about_deposit_without_discount_spec.rb
+++ b/spec/models/form/sales/pages/about_deposit_without_discount_spec.rb
@@ -1,12 +1,16 @@
 require "rails_helper"
 
 RSpec.describe Form::Sales::Pages::AboutDepositWithoutDiscount, type: :model do
-  subject(:page) { described_class.new(page_id, page_definition, subsection, ownershipsch: 1) }
+  subject(:page) { described_class.new(page_id, page_definition, subsection, ownershipsch: 1, optional: false) }
 
   let(:page_id) { nil }
   let(:page_definition) { nil }
   let(:subsection) { instance_double(Form::Subsection) }
 
+  before do
+    allow(subsection).to receive(:form).and_return(instance_double(Form, start_year_after_2024?: false))
+  end
+
   it "has correct subsection" do
     expect(page.subsection).to eq(subsection)
   end
@@ -34,4 +38,42 @@ RSpec.describe Form::Sales::Pages::AboutDepositWithoutDiscount, type: :model do
        { "ownershipsch" => 3, "mortgageused" => 1 }],
     )
   end
+
+  context "when optional is true" do
+    subject(:page) { described_class.new(page_id, page_definition, subsection, ownershipsch: 1, optional: true) }
+
+    it "has correct depends_on" do
+      expect(page.depends_on).to eq(
+        [{ "is_type_discount?" => false, "ownershipsch" => 1 },
+         { "ownershipsch" => 2 },
+         { "ownershipsch" => 3, "mortgageused" => 1 }],
+      )
+    end
+  end
+
+  context "when it's a 2024 form" do
+    before do
+      allow(subsection).to receive(:form).and_return(instance_double(Form, start_year_after_2024?: true))
+    end
+
+    it "has correct depends_on" do
+      expect(page.depends_on).to eq(
+        [{ "is_type_discount?" => false, "ownershipsch" => 1, "stairowned_100?" => false },
+         { "ownershipsch" => 2 },
+         { "ownershipsch" => 3, "mortgageused" => 1 }],
+      )
+    end
+
+    context "and optional is true" do
+      subject(:page) { described_class.new(page_id, page_definition, subsection, ownershipsch: 1, optional: true) }
+
+      it "has correct depends_on" do
+        expect(page.depends_on).to eq(
+          [{ "is_type_discount?" => false, "ownershipsch" => 1, "stairowned_100?" => true },
+           { "ownershipsch" => 2 },
+           { "ownershipsch" => 3, "mortgageused" => 1 }],
+        )
+      end
+    end
+  end
 end
diff --git a/spec/models/form/sales/questions/deposit_amount_spec.rb b/spec/models/form/sales/questions/deposit_amount_spec.rb
index e0a77b7fc..80429b5af 100644
--- a/spec/models/form/sales/questions/deposit_amount_spec.rb
+++ b/spec/models/form/sales/questions/deposit_amount_spec.rb
@@ -1,7 +1,7 @@
 require "rails_helper"
 
 RSpec.describe Form::Sales::Questions::DepositAmount, type: :model do
-  subject(:question) { described_class.new(question_id, question_definition, page, ownershipsch: 1) }
+  subject(:question) { described_class.new(question_id, question_definition, page, ownershipsch: 1, optional: false) }
 
   let(:question_id) { nil }
   let(:question_definition) { nil }
@@ -50,4 +50,12 @@ RSpec.describe Form::Sales::Questions::DepositAmount, type: :model do
   it "has correct max" do
     expect(question.max).to eq(999_999)
   end
+
+  context "when optional iis true" do
+    subject(:question) { described_class.new(question_id, question_definition, page, ownershipsch: 1, optional: true) }
+
+    it "has a correct hint_text" do
+      expect(question.hint_text).to eq("Enter the total cash sum paid by the buyer towards the property that was not funded by the mortgage. As this is a fully staircased sale this question is optional. If you do not have the information available click save and continue")
+    end
+  end
 end
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 192f7cbda..3746768d0 100644
--- a/spec/models/form/sales/subsections/shared_ownership_scheme_spec.rb
+++ b/spec/models/form/sales/subsections/shared_ownership_scheme_spec.rb
@@ -7,6 +7,10 @@ RSpec.describe Form::Sales::Subsections::SharedOwnershipScheme, type: :model do
   let(:subsection_definition) { nil }
   let(:section) { instance_double(Form::Sales::Sections::SaleInformation) }
 
+  before do
+    allow(section).to receive(:form).and_return(instance_double(Form, start_year_after_2024?: false))
+  end
+
   it "has correct section" do
     expect(shared_ownership_scheme.section).to eq(section)
   end
diff --git a/spec/models/validations/sales/sale_information_validations_spec.rb b/spec/models/validations/sales/sale_information_validations_spec.rb
index 73243e9fa..3d323112e 100644
--- a/spec/models/validations/sales/sale_information_validations_spec.rb
+++ b/spec/models/validations/sales/sale_information_validations_spec.rb
@@ -756,4 +756,48 @@ RSpec.describe Validations::Sales::SaleInformationValidations do
       end
     end
   end
+
+  describe "#validate_mortgage_used_and_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
+
+    context "when mortgageused don't know" do
+      let(:record) { build(:sales_log, ownershipsch: 1, type: 9, saledate: now, mortgageused: 3) }
+
+      it "does not add an error if stairowned 100" do
+        record.stairowned = 100
+        sale_information_validator.validate_mortgage_used_and_stairbought(record)
+
+        expect(record.errors).to be_empty
+      end
+
+      it "adds an error if stairowned is not 100" do
+        record.stairowned = 90
+        sale_information_validator.validate_mortgage_used_and_stairbought(record)
+
+        expect(record.errors[:stairowned]).to include("The percentage owned has to be 100% if the mortgage used is 'Don’t know'")
+        expect(record.errors[:mortgageused]).to include("The percentage owned has to be 100% if the mortgage used is 'Don’t know'")
+      end
+    end
+
+    context "when the collection year is before 2024" do
+      let(:record) { build(:sales_log, ownershipsch: 1, type: 9, saledate: now, mortgageused: 3, stairowned: 90) }
+      let(:now) { Time.zone.local(2023, 4, 4) }
+
+      it "does not add an error" do
+        sale_information_validator.validate_mortgage_used_and_stairbought(record)
+
+        expect(record.errors).to be_empty
+      end
+    end
+  end
 end
diff --git a/spec/services/bulk_upload/sales/year2024/row_parser_spec.rb b/spec/services/bulk_upload/sales/year2024/row_parser_spec.rb
index 93e6fdca1..d93453a22 100644
--- a/spec/services/bulk_upload/sales/year2024/row_parser_spec.rb
+++ b/spec/services/bulk_upload/sales/year2024/row_parser_spec.rb
@@ -975,6 +975,36 @@ RSpec.describe BulkUpload::Sales::Year2024::RowParser do
       end
     end
 
+    describe "#field_103" do # shared ownership mortgageused
+      context "when invalid value" do
+        let(:attributes) { setup_section_params.merge(field_103: "4") }
+
+        it "returns correct errors" do
+          expect(parser.errors[:field_103]).to include("Enter a valid value for Was a mortgage used for the purchase of this property? - Shared ownership")
+        end
+      end
+
+      context "when value is 3 and stairowned is not 100" do
+        let(:attributes) { setup_section_params.merge(field_103: "3", field_86: "1", field_87: "50", field_88: "99", field_109: nil) }
+
+        it "returns correct errors" do
+          expect(parser.errors[:field_103]).to include("Enter a valid value for Was a mortgage used for the purchase of this property? - Shared ownership")
+        end
+      end
+
+      context "when value is 3 and stairowned is 100" do
+        let(:attributes) { setup_section_params.merge(field_103: "3", field_86: "1", field_87: "50", field_88: "100", field_109: nil) }
+
+        it "does not add errors and sets mortgage used to 3" do
+          expect(parser.log.mortgageused).to be(3)
+          expect(parser.log.stairowned).to be(100)
+          expect(parser.log.deposit).to be(nil)
+          expect(parser.errors[:field_103]).to be_empty
+          expect(parser.errors[:field_109]).to be_empty
+        end
+      end
+    end
+
     describe "soft validations" do
       context "when soft validation is triggered" do
         let(:attributes) { valid_attributes.merge({ field_31: 22, field_35: 5 }) }