diff --git a/data/language/en-GB.txt b/data/language/en-GB.txt
index 40931282c0..7c61d5a50e 100644
--- a/data/language/en-GB.txt
+++ b/data/language/en-GB.txt
@@ -3647,6 +3647,8 @@ STR_6541    :{WINDOW_COLOUR_2}Rocky Mountain Construction Group, Josef Wiegand G
 STR_6542    :Contributors
 STR_6543    :Contributors…
 STR_6544    :Loan cannot be negative!
+STR_6545    :Use RCT1 interest calculation
+STR_6546    :Use the interest calculation algorithm of RollerCoaster Tycoon 1, which used a fixed percentage of approximately 1.33%.
 
 #############
 # Scenarios #
diff --git a/distribution/changelog.txt b/distribution/changelog.txt
index 9342f93d40..c9e22e15dc 100644
--- a/distribution/changelog.txt
+++ b/distribution/changelog.txt
@@ -8,6 +8,7 @@
 - Feature: [objects#226] Port RCT1 Corkscrew Coaster train.
 - Feature: [objects#229] Port RCT1 go karts with helmets.
 - Improved: [#11473] Hot reload for plug-ins now works on macOS.
+- Improved: [#12466] RCT1 parks now use RCT1’s interest calculation algorithm.
 - Improved: [#17288] Reorganise the order of shortcut keys in the Shortcut Keys window.
 - Improved: [#18706] Ability to view the list of contributors in-game.
 - Improved: [#18749] Ability to have 4 active awards for more than one month in a row.
diff --git a/src/openrct2-ui/windows/EditorScenarioOptions.cpp b/src/openrct2-ui/windows/EditorScenarioOptions.cpp
index 820d5763ad..d7c94ef098 100644
--- a/src/openrct2-ui/windows/EditorScenarioOptions.cpp
+++ b/src/openrct2-ui/windows/EditorScenarioOptions.cpp
@@ -80,6 +80,7 @@ enum {
     WIDX_INTEREST_RATE_INCREASE,
     WIDX_INTEREST_RATE_DECREASE,
     WIDX_FORBID_MARKETING,
+    WIDX_RCT1_INTEREST,
 
     // Guests tab
     WIDX_CASH_PER_GUEST = WIDX_PAGE_START,
@@ -130,6 +131,7 @@ static Widget window_editor_scenario_options_financial_widgets[] = {
     MakeSpinnerWidgets({168,  99}, {              100,  12}, WindowWidgetType::Spinner,  WindowColour::Secondary                                                            ), // NB: 3 widgets
     MakeSpinnerWidgets({168, 116}, {               70,  12}, WindowWidgetType::Spinner,  WindowColour::Secondary                                                            ), // NB: 3 widgets
     MakeWidget        ({  8, 133}, {WW_FINANCIAL - 16,  12}, WindowWidgetType::Checkbox, WindowColour::Secondary, STR_FORBID_MARKETING,   STR_FORBID_MARKETING_TIP          ),
+    MakeWidget        ({  8, 116}, {WW_FINANCIAL - 16,  12}, WindowWidgetType::Checkbox, WindowColour::Secondary, STR_RCT1_INTEREST,      STR_RCT1_INTEREST_TIP             ),
     WIDGETS_END,
 };
 
@@ -394,6 +396,14 @@ private:
                 Invalidate();
                 break;
             }
+            case WIDX_RCT1_INTEREST:
+            {
+                auto scenarioSetSetting = ScenarioSetSettingAction(
+                    ScenarioSetSetting::UseRCT1Interest, gParkFlags & PARK_FLAGS_RCT1_INTEREST ? 0 : 1);
+                GameActions::Execute(&scenarioSetSetting);
+                Invalidate();
+                break;
+            }
         }
     }
 
@@ -557,7 +567,7 @@ private:
         if (gParkFlags & PARK_FLAGS_NO_MONEY)
         {
             SetWidgetPressed(WIDX_NO_MONEY, true);
-            for (int32_t i = WIDX_INITIAL_CASH; i <= WIDX_FORBID_MARKETING; i++)
+            for (int32_t i = WIDX_INITIAL_CASH; i <= WIDX_RCT1_INTEREST; i++)
                 widgets[i].type = WindowWidgetType::Empty;
         }
         else
@@ -572,10 +582,23 @@ private:
             widgets[WIDX_MAXIMUM_LOAN].type = WindowWidgetType::Spinner;
             widgets[WIDX_MAXIMUM_LOAN_INCREASE].type = WindowWidgetType::Button;
             widgets[WIDX_MAXIMUM_LOAN_DECREASE].type = WindowWidgetType::Button;
-            widgets[WIDX_INTEREST_RATE].type = WindowWidgetType::Spinner;
-            widgets[WIDX_INTEREST_RATE_INCREASE].type = WindowWidgetType::Button;
-            widgets[WIDX_INTEREST_RATE_DECREASE].type = WindowWidgetType::Button;
             widgets[WIDX_FORBID_MARKETING].type = WindowWidgetType::Checkbox;
+
+            if (gParkFlags & PARK_FLAGS_RCT1_INTEREST)
+            {
+                widgets[WIDX_INTEREST_RATE].type = WindowWidgetType::Empty;
+                widgets[WIDX_INTEREST_RATE_INCREASE].type = WindowWidgetType::Empty;
+                widgets[WIDX_INTEREST_RATE_DECREASE].type = WindowWidgetType::Empty;
+                widgets[WIDX_RCT1_INTEREST].type = WindowWidgetType::Checkbox;
+                SetWidgetPressed(WIDX_RCT1_INTEREST, true);
+            }
+            else
+            {
+                widgets[WIDX_INTEREST_RATE].type = WindowWidgetType::Spinner;
+                widgets[WIDX_INTEREST_RATE_INCREASE].type = WindowWidgetType::Button;
+                widgets[WIDX_INTEREST_RATE_DECREASE].type = WindowWidgetType::Button;
+                widgets[WIDX_RCT1_INTEREST].type = WindowWidgetType::Empty;
+            }
         }
 
         SetWidgetPressed(WIDX_FORBID_MARKETING, gParkFlags & PARK_FLAGS_FORBID_MARKETING_CAMPAIGN);
diff --git a/src/openrct2-ui/windows/Finances.cpp b/src/openrct2-ui/windows/Finances.cpp
index 8de723064b..7a74041e5b 100644
--- a/src/openrct2-ui/windows/Finances.cpp
+++ b/src/openrct2-ui/windows/Finances.cpp
@@ -557,12 +557,15 @@ public:
 
         // Loan and interest rate
         DrawTextBasic(&dpi, windowPos + ScreenCoordsXY{ 8, 279 }, STR_FINANCES_SUMMARY_LOAN);
-        auto ft = Formatter();
-        ft.Add<uint16_t>(gBankLoanInterestRate);
-        DrawTextBasic(&dpi, windowPos + ScreenCoordsXY{ 167, 279 }, STR_FINANCES_SUMMARY_AT_X_PER_YEAR, ft);
+        if (!(gParkFlags & PARK_FLAGS_RCT1_INTEREST))
+        {
+            auto ft = Formatter();
+            ft.Add<uint16_t>(gBankLoanInterestRate);
+            DrawTextBasic(&dpi, windowPos + ScreenCoordsXY{ 167, 279 }, STR_FINANCES_SUMMARY_AT_X_PER_YEAR, ft);
+        }
 
         // Current cash
-        ft = Formatter();
+        auto ft = Formatter();
         ft.Add<money64>(gCash);
         StringId stringId = gCash >= 0 ? STR_CASH_LABEL : STR_CASH_NEGATIVE_LABEL;
         DrawTextBasic(&dpi, windowPos + ScreenCoordsXY{ 8, 294 }, stringId, ft);
diff --git a/src/openrct2/actions/ScenarioSetSettingAction.cpp b/src/openrct2/actions/ScenarioSetSettingAction.cpp
index 2a66f0c41f..3f018cc37b 100644
--- a/src/openrct2/actions/ScenarioSetSettingAction.cpp
+++ b/src/openrct2/actions/ScenarioSetSettingAction.cpp
@@ -246,6 +246,18 @@ GameActions::Result ScenarioSetSettingAction::Execute() const
         case ScenarioSetSetting::AllowEarlyCompletion:
             gAllowEarlyCompletionInNetworkPlay = _value;
             break;
+        case ScenarioSetSetting::UseRCT1Interest:
+        {
+            if (_value != 0)
+            {
+                gParkFlags |= PARK_FLAGS_RCT1_INTEREST;
+            }
+            else
+            {
+                gParkFlags &= ~PARK_FLAGS_RCT1_INTEREST;
+            }
+            break;
+        }
         default:
             LOG_ERROR("Invalid setting: %u", _setting);
             return GameActions::Result(GameActions::Status::InvalidParameters, STR_NONE, STR_NONE);
diff --git a/src/openrct2/actions/ScenarioSetSettingAction.h b/src/openrct2/actions/ScenarioSetSettingAction.h
index 948a44d54b..f0b74cd4c0 100644
--- a/src/openrct2/actions/ScenarioSetSettingAction.h
+++ b/src/openrct2/actions/ScenarioSetSettingAction.h
@@ -35,6 +35,7 @@ enum class ScenarioSetSetting : uint8_t
     ParkRatingHigherDifficultyLevel,
     GuestGenerationHigherDifficultyLevel,
     AllowEarlyCompletion,
+    UseRCT1Interest,
     Count
 };
 
diff --git a/src/openrct2/localisation/StringIds.h b/src/openrct2/localisation/StringIds.h
index bf0e8acd05..0d15d201a4 100644
--- a/src/openrct2/localisation/StringIds.h
+++ b/src/openrct2/localisation/StringIds.h
@@ -3941,6 +3941,9 @@ enum : uint16_t
 
     STR_LOAN_CANT_BE_NEGATIVE = 6544,
 
+    STR_RCT1_INTEREST = 6545,
+    STR_RCT1_INTEREST_TIP = 6546,
+
     // Have to include resource strings (from scenarios and objects) for the time being now that language is partially working
     /* MAX_STR_COUNT = 32768 */ // MAX_STR_COUNT - upper limit for number of strings, not the current count strings
 };
diff --git a/src/openrct2/management/Finance.cpp b/src/openrct2/management/Finance.cpp
index 6ed3cffd37..13620b516a 100644
--- a/src/openrct2/management/Finance.cpp
+++ b/src/openrct2/management/Finance.cpp
@@ -148,8 +148,9 @@ void FinancePayInterest()
     // This variable uses the 64-bit type as the computation below can involve multiplying very large numbers
     // that will overflow money32 if the loan is greater than (1 << 31) / (5 * current_interest_rate)
     const money64 current_loan = gBankLoan;
-    const uint8_t current_interest_rate = gBankLoanInterestRate;
-    const money32 interest_to_pay = (current_loan * 5 * current_interest_rate) >> 14;
+    const auto current_interest_rate = gBankLoanInterestRate;
+    const money32 interest_to_pay = (gParkFlags & PARK_FLAGS_RCT1_INTEREST) ? (current_loan / 2400)
+                                                                            : (current_loan * 5 * current_interest_rate) >> 14;
 
     FinancePayment(interest_to_pay, ExpenditureType::Interest);
 }
diff --git a/src/openrct2/network/NetworkBase.cpp b/src/openrct2/network/NetworkBase.cpp
index c2e281fa1f..66aa7596ed 100644
--- a/src/openrct2/network/NetworkBase.cpp
+++ b/src/openrct2/network/NetworkBase.cpp
@@ -43,7 +43,7 @@
 // It is used for making sure only compatible builds get connected, even within
 // single OpenRCT2 version.
 
-#define NETWORK_STREAM_VERSION "5"
+#define NETWORK_STREAM_VERSION "6"
 
 #define NETWORK_STREAM_ID OPENRCT2_VERSION "-" NETWORK_STREAM_VERSION
 
diff --git a/src/openrct2/rct1/S4Importer.cpp b/src/openrct2/rct1/S4Importer.cpp
index 6386765191..4ae86c35a1 100644
--- a/src/openrct2/rct1/S4Importer.cpp
+++ b/src/openrct2/rct1/S4Importer.cpp
@@ -2203,6 +2203,7 @@ namespace RCT1
             // Flags
             gParkFlags = _s4.ParkFlags;
             gParkFlags &= ~PARK_FLAGS_ANTI_CHEAT_DEPRECATED;
+            gParkFlags |= PARK_FLAGS_RCT1_INTEREST;
             // Loopy Landscape parks can set a flag to lock the entry price to free.
             // If this flag is not set, the player can ask money for both rides and entry.
             if (!(_s4.ParkFlags & RCT1_PARK_FLAGS_PARK_ENTRY_LOCKED_AT_FREE))
diff --git a/src/openrct2/world/Park.h b/src/openrct2/world/Park.h
index 43d74876f7..5c6496d8c2 100644
--- a/src/openrct2/world/Park.h
+++ b/src/openrct2/world/Park.h
@@ -40,7 +40,9 @@ enum : uint32_t
     PARK_FLAGS_NO_MONEY_SCENARIO = (1 << 17),                 // Deprecated, originally used in scenario editor
     PARK_FLAGS_SPRITES_INITIALISED = (1 << 18),  // After a scenario is loaded this prevents edits in the scenario editor
     PARK_FLAGS_SIX_FLAGS_DEPRECATED = (1 << 19), // Not used anymore
-    PARK_FLAGS_UNLOCK_ALL_PRICES = (1u << 31),   // OpenRCT2 only!
+
+    PARK_FLAGS_RCT1_INTEREST = (1u << 30),     // OpenRCT2 only
+    PARK_FLAGS_UNLOCK_ALL_PRICES = (1u << 31), // OpenRCT2 only
 };
 
 struct Guest;