diff --git a/domain/sap10_calculator/tables/table_12a.py b/domain/sap10_calculator/tables/table_12a.py
index e4a07f1b..f98e1c27 100644
--- a/domain/sap10_calculator/tables/table_12a.py
+++ b/domain/sap10_calculator/tables/table_12a.py
@@ -83,6 +83,11 @@ _METER_STR_TO_INT: Final[dict[str, int]] = {
     "dual": 1,
     "dual (24 hour)": 4,
     "off-peak 18 hour": 5,
+    # RdSAP 10 §17 page 85 row 10-2 lodging form: "18-hour" (Elmhurst
+    # Summary §14.2 surfaces this as the bare "18 Hour"). Per §12
+    # page 62: "if the meter is dual 18-hour/24-hour it is 18-hour/
+    # 24-hour tariff" → enum 5 (EIGHTEEN_HOUR).
+    "18 hour": 5,
     "unknown": 3,
     "": 3,
 }
diff --git a/domain/sap10_calculator/tests/test_table_12a.py b/domain/sap10_calculator/tests/test_table_12a.py
index 3135881e..2b294ca2 100644
--- a/domain/sap10_calculator/tests/test_table_12a.py
+++ b/domain/sap10_calculator/tests/test_table_12a.py
@@ -51,6 +51,13 @@ def test_tariff_enum_has_five_members() -> None:
         ("Dual", Tariff.SEVEN_HOUR),
         ("Dual (24 hour)", Tariff.TWENTY_FOUR_HOUR),
         ("Off-peak 18 hour", Tariff.EIGHTEEN_HOUR),
+        # RdSAP 10 §17 page 85 (Electricity meter row 10-2):
+        # "Dual/single/10-hour/18-hour/24-hour/unknown". The Elmhurst
+        # Summary §14.2 lodges the bare form "18 Hour" (not the
+        # "Off-peak 18 hour" alias above). Per §12 page 62: "if the
+        # meter is dual 18-hour/24-hour it is 18-hour/24-hour tariff",
+        # so the bare lodging routes directly to EIGHTEEN_HOUR.
+        ("18 Hour", Tariff.EIGHTEEN_HOUR),
         # Per Q11b: "Unknown" maps to STANDARD (no off-peak heuristic).
         ("Unknown", Tariff.STANDARD),
         ("", Tariff.STANDARD),