diff --git a/heat-stack/app/utils/pyodide.test.ts b/heat-stack/app/utils/pyodide.test.ts
index 16e7cd17..1dff3364 100644
--- a/heat-stack/app/utils/pyodide.test.ts
+++ b/heat-stack/app/utils/pyodide.test.ts
@@ -220,7 +220,6 @@ test('pyodide solves climate change', async () => {
     }
 
     const executePy = await pyodide.runPythonAsync(`
-    from datetime import date
     from rules_engine import parser
     from rules_engine.pydantic_models import (
         FuelType,
@@ -238,7 +237,7 @@ test('pyodide solves climate change', async () => {
 
 
         summaryInput = SummaryInput(**summaryInputFromJs)
-        temperatureInput = TemperatureInput(dates=[date.fromisoformat(date_) for date_ in temperatureInputFromJs["dates"]], temperatures=temperatureInputFromJs["temperatures"])
+        temperatureInput = TemperatureInput(**temperatureInputFromJs)
 
         outputs = engine.get_outputs_natural_gas(summaryInput,temperatureInput, naturalGasInputRecords)
 
diff --git a/rules-engine/src/rules_engine/pydantic_models.py b/rules-engine/src/rules_engine/pydantic_models.py
index 6c98921f..fce42087 100644
--- a/rules-engine/src/rules_engine/pydantic_models.py
+++ b/rules-engine/src/rules_engine/pydantic_models.py
@@ -171,8 +171,12 @@ class NormalizedBillingPeriodRecord(NormalizedBillingPeriodRecordBase):
     whole_home_heat_loss_rate: Optional[float] = Field(frozen=True)
 
 
+def _date_string_parser(rate: str) -> datetime:
+    return datetime.strptime(rate, "%Y-%m-%d")
+
+
 class TemperatureInput(BaseModel):
-    dates: list[datetime]
+    dates: list[Annotated[datetime, BeforeValidator(_date_string_parser)]]
     temperatures: list[float]
 
 
diff --git a/rules-engine/tests/test_rules_engine/test_engine.py b/rules-engine/tests/test_rules_engine/test_engine.py
index 17ae1e0f..40ca3346 100644
--- a/rules-engine/tests/test_rules_engine/test_engine.py
+++ b/rules-engine/tests/test_rules_engine/test_engine.py
@@ -185,7 +185,7 @@ def sample_temp_inputs() -> TemperatureInput:
 
     return TemperatureInput(
         temperatures=temperature_dict["temperatures"],
-        dates=[datetime.fromisoformat(x) for x in temperature_dict["dates"]],
+        dates=temperature_dict["dates"],
     )
 
 
diff --git a/rules-engine/tests/test_rules_engine/test_utils.py b/rules-engine/tests/test_rules_engine/test_utils.py
index 57c622f4..32a6c81b 100644
--- a/rules-engine/tests/test_rules_engine/test_utils.py
+++ b/rules-engine/tests/test_rules_engine/test_utils.py
@@ -172,7 +172,7 @@ def load_temperature_data(path: Path, weather_station: str) -> TemperatureInput:
 
         row: Any
         for row in reader:
-            dates.append(datetime.strptime(row["Date"], "%Y-%m-%d"))
+            dates.append(row["Date"])
             temperatures.append(row[weather_station])
 
     return TemperatureInput(dates=dates, temperatures=temperatures)