diff --git a/packages/domain/src/domain/sap/calculator.py b/packages/domain/src/domain/sap/calculator.py
index 3c63f46d..3fc4c625 100644
--- a/packages/domain/src/domain/sap/calculator.py
+++ b/packages/domain/src/domain/sap/calculator.py
@@ -190,7 +190,20 @@ class CalculatorInputs:
     # three collapse to the same value.
     space_heating_primary_factor: float = 1.0
     hot_water_primary_factor: float = 1.0
-    other_primary_factor: float = 1.969  # standard-electricity PEF (SAP 10.2)
+    # Standard-electricity PE factor per RdSAP10 Table 32 (p.95) / SAP10.2
+    # Table 12 = 1.501. Table 12e (p.195) provides monthly overrides — see
+    # the per-end-use PE factor fields below for the monthly cascade.
+    other_primary_factor: float = 1.501
+    # Per-end-use effective PE factors. For electricity end-uses with known
+    # monthly kWh distribution, cert_to_inputs computes the days-weighted
+    # Table 12e factor Σ(kWh_m × PE_m) / Σ(kWh_m). Gas end-uses keep the
+    # annual Table 12 factor. None → calculator falls back to the global
+    # `space_heating_primary_factor` / `hot_water_primary_factor` /
+    # `other_primary_factor` (legacy synthetic path).
+    secondary_heating_primary_factor: Optional[float] = None
+    pumps_fans_primary_factor: Optional[float] = None
+    lighting_primary_factor: Optional[float] = None
+    electric_shower_primary_factor: Optional[float] = None
     # Generation offsets — applied as a cost credit against the ECF
     # numerator. SAP 10.2 Appendix M: PV self-consumption + export
     # collapse to a single credit at the export rate (Table 12 code 60).
@@ -460,16 +473,44 @@ def calculate_sap_from_inputs(inputs: CalculatorInputs) -> SapResult:
         + electric_shower_co2
     )
 
+    # Per-end-use effective PE factors. Same shape as the CO2 cascade:
+    # electricity end-uses use Table 12e (p.195) monthly factors weighted
+    # by per-month kWh; gas end-uses use the annual Table 12 / Table 32
+    # PE factor. Defaults fall back to the legacy single-factor path so
+    # synthetic CalculatorInputs constructions keep working.
+    secondary_primary_factor = (
+        inputs.secondary_heating_primary_factor
+        if inputs.secondary_heating_primary_factor is not None
+        else inputs.space_heating_primary_factor
+    )
+    pumps_fans_primary_factor = (
+        inputs.pumps_fans_primary_factor
+        if inputs.pumps_fans_primary_factor is not None
+        else inputs.other_primary_factor
+    )
+    lighting_primary_factor = (
+        inputs.lighting_primary_factor
+        if inputs.lighting_primary_factor is not None
+        else inputs.other_primary_factor
+    )
+    electric_shower_primary_factor = (
+        inputs.electric_shower_primary_factor
+        if inputs.electric_shower_primary_factor is not None
+        else inputs.other_primary_factor
+    )
     space_heating_primary_kwh = (
-        main_fuel_kwh + secondary_fuel_kwh
-    ) * inputs.space_heating_primary_factor
+        main_fuel_kwh * inputs.space_heating_primary_factor
+        + secondary_fuel_kwh * secondary_primary_factor
+    )
     hot_water_primary_kwh = inputs.hot_water_kwh_per_yr * inputs.hot_water_primary_factor
     other_primary_kwh = (
-        inputs.pumps_fans_kwh_per_yr + inputs.lighting_kwh_per_yr
-    ) * inputs.other_primary_factor
-    # PV offsets primary energy at the same PEF (Appendix M: export PEF =
-    # standard-electricity PEF for ratings, since the displaced grid kWh
-    # would have been imported electricity).
+        inputs.pumps_fans_kwh_per_yr * pumps_fans_primary_factor
+        + inputs.lighting_kwh_per_yr * lighting_primary_factor
+        + inputs.electric_shower_kwh_per_yr * electric_shower_primary_factor
+    )
+    # PV offsets primary energy at the export PEF (Table 32 code 60 =
+    # 0.501 — half the import PEF since exported kWh isn't subject to the
+    # full grid-loss multiplier).
     pv_primary_offset_kwh = inputs.pv_generation_kwh_per_yr * inputs.other_primary_factor
     primary_energy_kwh = max(
         0.0,
diff --git a/packages/domain/src/domain/sap/rdsap/cert_to_inputs.py b/packages/domain/src/domain/sap/rdsap/cert_to_inputs.py
index 6175a0b2..80a5d6f8 100644
--- a/packages/domain/src/domain/sap/rdsap/cert_to_inputs.py
+++ b/packages/domain/src/domain/sap/rdsap/cert_to_inputs.py
@@ -58,6 +58,7 @@ from domain.sap.tables.pcdb.parser import GasOilBoilerRecord
 from domain.sap.tables.table_12 import (
     co2_monthly_factors_kg_per_kwh,
     co2_factor_kg_per_kwh,
+    pe_monthly_factors_kwh_per_kwh,
     primary_energy_factor,
     unit_price_p_per_kwh,
 )
@@ -728,15 +729,16 @@ def _water_efficiency_with_category_inherit(
 
 
 
-def _effective_monthly_co2_factor(
-    monthly_kwh: tuple[float, ...], fuel_code: int
+def _effective_monthly_factor(
+    monthly_kwh: tuple[float, ...],
+    monthly_factors: Optional[tuple[float, ...]],
 ) -> Optional[float]:
-    """SAP 10.2 Table 12d (p.194): for electricity end-uses, the effective
-    annual CO2 factor is Σ(kWh_m × CO2_m) / Σ(kWh_m). Returns None for non-
-    electricity fuels or when total kWh is zero (caller falls back to the
-    annual Table 12 factor). Used to translate monthly Table 12d cascade
-    into the calculator's annual × factor shape without restructuring."""
-    monthly_factors = co2_monthly_factors_kg_per_kwh(fuel_code)
+    """Days-weighted effective annual factor = Σ(kWh_m × factor_m) / Σ kWh_m.
+
+    Used to translate SAP 10.2 Table 12d (CO2) and Table 12e (PE) monthly
+    cascades into the calculator's annual × factor shape. Returns None
+    when factors are None (non-electricity fuel — caller falls back to the
+    annual Table 12 factor) or when total kWh is zero."""
     if monthly_factors is None:
         return None
     total_kwh = sum(monthly_kwh)
@@ -745,6 +747,26 @@ def _effective_monthly_co2_factor(
     return sum(k * f for k, f in zip(monthly_kwh, monthly_factors)) / total_kwh
 
 
+def _effective_monthly_co2_factor(
+    monthly_kwh: tuple[float, ...], fuel_code: int
+) -> Optional[float]:
+    """SAP 10.2 Table 12d (p.194) monthly CO2 cascade. Thin wrapper over
+    `_effective_monthly_factor` for the CO2 lookup."""
+    return _effective_monthly_factor(
+        monthly_kwh, co2_monthly_factors_kg_per_kwh(fuel_code)
+    )
+
+
+def _effective_monthly_pe_factor(
+    monthly_kwh: tuple[float, ...], fuel_code: int
+) -> Optional[float]:
+    """SAP 10.2 Table 12e (p.195) monthly PE cascade. Thin wrapper over
+    `_effective_monthly_factor` for the PE lookup."""
+    return _effective_monthly_factor(
+        monthly_kwh, pe_monthly_factors_kwh_per_kwh(fuel_code)
+    )
+
+
 def _days_in_month_proportioned(
     annual_kwh: float, days_in_month: tuple[int, ...]
 ) -> tuple[float, ...]:
@@ -2019,6 +2041,26 @@ def cert_to_inputs(
             epc.sap_heating.water_heating_fuel or main_fuel
         ),
         other_primary_factor=primary_energy_factor(30),  # standard electricity
+        # SAP 10.2 Table 12e (p.195) per-end-use effective PE factors. Same
+        # shape as the Table 12d CO2 cascade: electricity end-uses use the
+        # monthly factors weighted by per-month kWh; gas end-uses pass
+        # through the annual Table 12 / Table 32 PE factor. Secondary
+        # defaults to standard electricity per RdSAP §A.2.2.
+        secondary_heating_primary_factor=_effective_monthly_pe_factor(
+            energy_requirements_result.secondary_fuel_monthly_kwh,
+            _STANDARD_ELECTRICITY_FUEL_CODE,
+        ),
+        pumps_fans_primary_factor=_effective_monthly_pe_factor(
+            _days_in_month_proportioned(pumps_fans_kwh, _DAYS_IN_MONTH),
+            _STANDARD_ELECTRICITY_FUEL_CODE,
+        ),
+        lighting_primary_factor=_effective_monthly_pe_factor(
+            lighting_monthly_kwh, _STANDARD_ELECTRICITY_FUEL_CODE,
+        ),
+        electric_shower_primary_factor=_effective_monthly_pe_factor(
+            wh_result.electric_shower_monthly_kwh if wh_result is not None else (0.0,) * 12,
+            _STANDARD_ELECTRICITY_FUEL_CODE,
+        ),
         fuel_cost=_fuel_cost(
             epc=epc,
             main=main,
diff --git a/packages/domain/src/domain/sap/tables/table_12.py b/packages/domain/src/domain/sap/tables/table_12.py
index 63b6af14..78c55488 100644
--- a/packages/domain/src/domain/sap/tables/table_12.py
+++ b/packages/domain/src/domain/sap/tables/table_12.py
@@ -127,6 +127,54 @@ def co2_monthly_factors_kg_per_kwh(fuel_code: int | None) -> Optional[tuple[floa
     return None
 
 
+# SAP 10.2 Table 12e (p.195) — monthly variation in PE (primary energy)
+# emission factors for electricity. Spec text: "Where electricity is the
+# fuel used, the relevant set of factors in the table below should be
+# used to calculate the monthly primary energy instead the annual average
+# factor given in Table 12." Same shape as Table 12d (CO2): electricity
+# end-uses use Σ(kWh_m × PE_m); gas/non-electricity fuels keep the
+# annual Table 12 PE factor.
+PE_FACTOR_MONTHLY: Final[dict[int, tuple[float, ...]]] = {
+    # Standard tariff
+    30: (1.602, 1.593, 1.568, 1.530, 1.487, 1.441, 1.410, 1.413, 1.449, 1.504, 1.558, 1.604),
+    # 7-hour tariff
+    32: (1.635, 1.626, 1.600, 1.562, 1.518, 1.471, 1.440, 1.443, 1.479, 1.535, 1.591, 1.637),
+    31: (1.521, 1.512, 1.488, 1.453, 1.411, 1.368, 1.339, 1.342, 1.376, 1.428, 1.480, 1.522),
+    # 10-hour tariff
+    34: (1.625, 1.615, 1.590, 1.552, 1.507, 1.462, 1.430, 1.433, 1.470, 1.525, 1.580, 1.626),
+    33: (1.571, 1.561, 1.537, 1.500, 1.457, 1.413, 1.382, 1.386, 1.421, 1.474, 1.528, 1.572),
+    # 18-hour tariff (matches standard tariff)
+    38: (1.602, 1.593, 1.568, 1.530, 1.487, 1.441, 1.410, 1.413, 1.449, 1.504, 1.558, 1.604),
+    40: (1.602, 1.593, 1.568, 1.530, 1.487, 1.441, 1.410, 1.413, 1.449, 1.504, 1.558, 1.604),
+    # 24-hour heating tariff
+    35: (1.602, 1.593, 1.568, 1.530, 1.487, 1.441, 1.410, 1.413, 1.449, 1.504, 1.558, 1.604),
+    # Electricity sold to grid (PV) — note (i): deducted, low PE factor
+    60: (0.715, 0.697, 0.645, 0.567, 0.478, 0.389, 0.330, 0.336, 0.405, 0.513, 0.623, 0.718),
+    # Electricity sold to grid, other
+    36: (0.602, 0.593, 0.568, 0.530, 0.487, 0.441, 0.410, 0.413, 0.449, 0.504, 0.558, 0.604),
+    # Electricity, any tariff
+    39: (1.602, 1.593, 1.568, 1.530, 1.487, 1.441, 1.410, 1.413, 1.449, 1.504, 1.558, 1.604),
+    # Heat from electric heat pump
+    41: (1.602, 1.593, 1.568, 1.530, 1.487, 1.441, 1.410, 1.413, 1.449, 1.504, 1.558, 1.604),
+    # Low-grade heat recovered from process
+    49: (1.602, 1.593, 1.568, 1.530, 1.487, 1.441, 1.410, 1.413, 1.449, 1.504, 1.558, 1.604),
+    # Electricity for pumping in distribution network
+    50: (1.602, 1.593, 1.568, 1.530, 1.487, 1.441, 1.410, 1.413, 1.449, 1.504, 1.558, 1.604),
+}
+
+
+def pe_monthly_factors_kwh_per_kwh(
+    fuel_code: int | None,
+) -> Optional[tuple[float, ...]]:
+    """SAP 10.2 Table 12e (p.195) monthly PE factors for electricity. Returns
+    None for non-electricity fuels (use the annual `primary_energy_factor`)."""
+    if fuel_code is None:
+        return None
+    if fuel_code in PE_FACTOR_MONTHLY:
+        return PE_FACTOR_MONTHLY[fuel_code]
+    return None
+
+
 CO2_KG_PER_KWH: Final[dict[int, float]] = {
     # Gas fuels
     1: 0.210,