diff --git a/changelog_entry.yaml b/changelog_entry.yaml
index e69de29b..09010966 100644
--- a/changelog_entry.yaml
+++ b/changelog_entry.yaml
@@ -0,0 +1,4 @@
+- bump: minor
+  changes:
+    added:
+    - Default input and output periods to Simulation constructor.
diff --git a/policyengine_core/simulations/simulation.py b/policyengine_core/simulations/simulation.py
index 472ea636..795642fc 100644
--- a/policyengine_core/simulations/simulation.py
+++ b/policyengine_core/simulations/simulation.py
@@ -89,7 +89,15 @@ def __init__(
         dataset: Union[str, Type[Dataset]] = None,
         reform: Reform = None,
         trace: bool = False,
+        default_input_period: str = None,
+        default_calculation_period: str = None,
     ):
+        self.default_input_period = (
+            default_input_period or self.default_input_period
+        )
+        self.default_calculation_period = (
+            default_calculation_period or self.default_calculation_period
+        )
         if tax_benefit_system is None:
             if (
                 self.default_tax_benefit_system_instance is not None