diff --git a/domain/sap10_calculator/calculator.py b/domain/sap10_calculator/calculator.py
index 45dbb921..ff634c8f 100644
--- a/domain/sap10_calculator/calculator.py
+++ b/domain/sap10_calculator/calculator.py
@@ -300,6 +300,13 @@ class CalculatorInputs:
     fuel_cost: FuelCostResult = field(
         default_factory=lambda: _ZERO_FUEL_COST_RESULT
     )
+    # Table 32 standing charges (electric off-peak high-rate code +
+    # mains gas) — added to `total_cost` when the calculator's off-
+    # peak fallback path fires. STANDARD-tariff certs route through
+    # `fuel_cost.additional_standing_charges_gbp` instead and ignore
+    # this field. cert_to_inputs sets this via `additional_standing_
+    # charges_gbp(main_fuel_code, water_heating_fuel_code, tariff)`.
+    standing_charges_gbp: float = 0.0
 
 
 @dataclass(frozen=True)
@@ -518,6 +525,7 @@ def calculate_sap_from_inputs(inputs: CalculatorInputs) -> SapResult:
             + hot_water_cost
             + pumps_fans_cost
             + lighting_cost
+            + inputs.standing_charges_gbp
             - pv_credit,
         )
     ecf = energy_cost_factor(total_cost_gbp=total_cost, total_floor_area_m2=tfa)
diff --git a/domain/sap10_calculator/rdsap/cert_to_inputs.py b/domain/sap10_calculator/rdsap/cert_to_inputs.py
index db1ac05f..69b46f15 100644
--- a/domain/sap10_calculator/rdsap/cert_to_inputs.py
+++ b/domain/sap10_calculator/rdsap/cert_to_inputs.py
@@ -3405,6 +3405,15 @@ def cert_to_inputs(
         other_fuel_cost_gbp_per_kwh=_other_fuel_cost_gbp_per_kwh(
             _rdsap_tariff(epc), prices
         ),
+        # Table 32 standing charges for the off-peak fallback path.
+        # STANDARD-tariff certs route via `fuel_cost.additional_
+        # standing_charges_gbp` (set inside `_fuel_cost`) and the
+        # calculator ignores this scalar on that path.
+        standing_charges_gbp=additional_standing_charges_gbp(
+            main_fuel_code=_main_fuel_code(main),
+            water_heating_fuel_code=_water_heating_fuel_code(epc),
+            tariff=_rdsap_tariff(epc),
+        ),
         co2_factor_kg_per_kwh=_co2_factor_kg_per_kwh(main),
         # SAP10.2 Table 12d (p.194) per-end-use effective CO2 factors. For
         # electricity end-uses Σ(kWh_m × CO2_m) / Σ(kWh_m) replaces the