diff --git a/app/models/validations/sales/financial_validations.rb b/app/models/validations/sales/financial_validations.rb
index 410f6d250..bc1ca95cf 100644
--- a/app/models/validations/sales/financial_validations.rb
+++ b/app/models/validations/sales/financial_validations.rb
@@ -92,6 +92,20 @@ module Validations::Sales::FinancialValidations
     end
   end
 
+  def validate_shared_ownership_deposit(record)
+    return unless record.saledate && record.form.start_year_after_2024?
+    return unless record.mortgage || record.mortgageused == 2 || record.mortgageused == 3
+    return unless record.cashdis && record.deposit && record.value && record.equity
+
+    mortgage_value = record.mortgage || 0
+
+    if mortgage_value + record.deposit + record.cashdis != record.value * record.equity / 100
+      %i[mortgage value deposit ownershipsch cashdis equity].each do |field|
+        record.errors.add field, I18n.t("validations.financial.shared_ownership_deposit", mortgage_deposit_and_discount_error_fields: record.mortgage_deposit_and_discount_error_fields, mortgage_deposit_and_discount_total: record.field_formatted_as_currency("mortgage_deposit_and_discount_total"))
+      end
+    end
+  end
+
 private
 
   def is_relationship_child?(relationship)
diff --git a/config/locales/en.yml b/config/locales/en.yml
index 8a3e8cd77..eb2a17ce5 100644
--- a/config/locales/en.yml
+++ b/config/locales/en.yml
@@ -433,6 +433,7 @@ en:
         under_min: "The minimum initial equity stake for this type of shared ownership sale is %{min_equity}%"
         over_max: "The maximum initial equity stake is %{max_equity}%"
       mortgage: "Mortgage value cannot be £0 if a mortgage was used for the purchase of this property"
+      shared_ownership_deposit: "You told us that the %{mortgage_deposit_and_discount_error_fields} add up to %{mortgage_deposit_and_discount_total}"
 
     household:
       reasonable_preference_reason:
diff --git a/spec/models/validations/sales/financial_validations_spec.rb b/spec/models/validations/sales/financial_validations_spec.rb
index 68cf19a14..873903c56 100644
--- a/spec/models/validations/sales/financial_validations_spec.rb
+++ b/spec/models/validations/sales/financial_validations_spec.rb
@@ -339,4 +339,179 @@ RSpec.describe Validations::Sales::FinancialValidations do
       end
     end
   end
+
+  describe "#validate_shared_ownership_deposit" do
+    let(:record) { FactoryBot.create(:sales_log, saledate: now) }
+
+    around do |example|
+      Timecop.freeze(now) do
+        Singleton.__init__(FormHandler)
+        example.run
+      end
+      Timecop.return
+    end
+
+    context "with a log in the 24/25 collection year" do
+      let(:now) { Time.zone.local(2024, 4, 2) }
+
+      it "does not add an error if MORTGAGE + DEPOSIT + CASHDIS are equal VALUE * EQUITY/100" do
+        record.mortgage = 1000
+        record.deposit = 1000
+        record.cashdis = 1000
+        record.value = 3000
+        record.equity = 100
+
+        financial_validator.validate_shared_ownership_deposit(record)
+        expect(record.errors["mortgage"]).to be_empty
+        expect(record.errors["deposit"]).to be_empty
+        expect(record.errors["cashdis"]).to be_empty
+        expect(record.errors["value"]).to be_empty
+        expect(record.errors["equity"]).to be_empty
+      end
+
+      it "does not add an error if mortgage is used and no mortgage is given" do
+        record.mortgage = nil
+        record.deposit = 1000
+        record.cashdis = 1000
+        record.value = 3000
+        record.equity = 100
+
+        financial_validator.validate_shared_ownership_deposit(record)
+        expect(record.errors["mortgage"]).to be_empty
+        expect(record.errors["deposit"]).to be_empty
+        expect(record.errors["cashdis"]).to be_empty
+        expect(record.errors["value"]).to be_empty
+        expect(record.errors["equity"]).to be_empty
+      end
+
+      it "adds an error if mortgage is not used and no mortgage is given" do
+        record.mortgage = nil
+        record.mortgageused = 2
+        record.deposit = 1000
+        record.cashdis = 1000
+        record.value = 3000
+        record.equity = 100
+
+        financial_validator.validate_shared_ownership_deposit(record)
+        expect(record.errors["mortgage"]).to include("You told us that the mortgage, deposit, and discount add up to £2,000.00")
+        expect(record.errors["deposit"]).to include("You told us that the mortgage, deposit, and discount add up to £2,000.00")
+        expect(record.errors["cashdis"]).to include("You told us that the mortgage, deposit, and discount add up to £2,000.00")
+        expect(record.errors["value"]).to include("You told us that the mortgage, deposit, and discount add up to £2,000.00")
+        expect(record.errors["equity"]).to include("You told us that the mortgage, deposit, and discount add up to £2,000.00")
+      end
+
+      it "does not add an error if no deposit is given" do
+        record.mortgage = 1000
+        record.deposit = nil
+        record.cashdis = 1000
+        record.value = 3000
+        record.equity = 100
+
+        financial_validator.validate_shared_ownership_deposit(record)
+        expect(record.errors["mortgage"]).to be_empty
+        expect(record.errors["deposit"]).to be_empty
+        expect(record.errors["cashdis"]).to be_empty
+        expect(record.errors["value"]).to be_empty
+        expect(record.errors["equity"]).to be_empty
+      end
+
+      it "does not add an error if no cashdis is given and cashdis is routed to" do
+        record.mortgage = 1000
+        record.deposit = 1000
+        record.type = 18
+        record.cashdis = nil
+        record.value = 3000
+        record.equity = 100
+
+        financial_validator.validate_shared_ownership_deposit(record)
+        expect(record.errors["mortgage"]).to be_empty
+        expect(record.errors["deposit"]).to be_empty
+        expect(record.errors["cashdis"]).to be_empty
+        expect(record.errors["value"]).to be_empty
+        expect(record.errors["equity"]).to be_empty
+      end
+
+      it "does not add an error if no cashdis is given and cashdis is not routed to" do
+        record.mortgageused = 1
+        record.mortgage = 1000
+        record.deposit = 1000
+        record.type = 2
+        record.cashdis = nil
+        record.value = 3000
+        record.equity = 100
+
+        financial_validator.validate_shared_ownership_deposit(record)
+        expect(record.errors["mortgage"]).to be_empty
+        expect(record.errors["deposit"]).to be_empty
+        expect(record.errors["cashdis"]).to be_empty
+        expect(record.errors["value"]).to be_empty
+        expect(record.errors["equity"]).to be_empty
+      end
+
+      it "does not add an error if no value is given" do
+        record.mortgage = 1000
+        record.deposit = 1000
+        record.cashdis = 1000
+        record.value = nil
+        record.equity = 100
+
+        financial_validator.validate_shared_ownership_deposit(record)
+        expect(record.errors["mortgage"]).to be_empty
+        expect(record.errors["deposit"]).to be_empty
+        expect(record.errors["cashdis"]).to be_empty
+        expect(record.errors["value"]).to be_empty
+        expect(record.errors["equity"]).to be_empty
+      end
+
+      it "does not add an error if no equity is given" do
+        record.mortgage = 1000
+        record.deposit = 1000
+        record.cashdis = 1000
+        record.value = 3000
+        record.equity = nil
+
+        financial_validator.validate_shared_ownership_deposit(record)
+        expect(record.errors["mortgage"]).to be_empty
+        expect(record.errors["deposit"]).to be_empty
+        expect(record.errors["cashdis"]).to be_empty
+        expect(record.errors["value"]).to be_empty
+        expect(record.errors["equity"]).to be_empty
+      end
+
+      it "adds an error if MORTGAGE + DEPOSIT + CASHDIS are not equal VALUE * EQUITY/100" do
+        record.mortgageused = 1
+        record.mortgage = 1000
+        record.deposit = 1000
+        record.cashdis = 1000
+        record.value = 4323
+        record.equity = 100
+
+        financial_validator.validate_shared_ownership_deposit(record)
+        expect(record.errors["mortgage"]).to include("You told us that the mortgage, deposit, and discount add up to £3,000.00")
+        expect(record.errors["deposit"]).to include("You told us that the mortgage, deposit, and discount add up to £3,000.00")
+        expect(record.errors["cashdis"]).to include("You told us that the mortgage, deposit, and discount add up to £3,000.00")
+        expect(record.errors["value"]).to include("You told us that the mortgage, deposit, and discount add up to £3,000.00")
+        expect(record.errors["equity"]).to include("You told us that the mortgage, deposit, and discount add up to £3,000.00")
+      end
+    end
+
+    context "with a log in 23/24 collection year" do
+      let(:now) { Time.zone.local(2024, 1, 1) }
+
+      it "does not add an error if MORTGAGE + DEPOSIT + CASHDIS are not equal VALUE * EQUITY/100" do
+        record.mortgage = 1000
+        record.deposit = 1000
+        record.cashdis = 1000
+        record.value = 4323
+        record.equity = 100
+
+        financial_validator.validate_shared_ownership_deposit(record)
+        expect(record.errors["mortgage"]).to be_empty
+        expect(record.errors["deposit"]).to be_empty
+        expect(record.errors["cashdis"]).to be_empty
+        expect(record.errors["value"]).to be_empty
+        expect(record.errors["equity"]).to be_empty
+      end
+    end
+  end
 end