diff --git a/causalpy/pymc_experiments.py b/causalpy/pymc_experiments.py
index 1c07e189..30073e3c 100644
--- a/causalpy/pymc_experiments.py
+++ b/causalpy/pymc_experiments.py
@@ -164,8 +164,8 @@ def __init__(
         # set experiment type - usually done in subclasses
         self.expt_type = "Pre-Post Fit"
         # split data in to pre and post intervention
-        self.datapre = data[data.index <= self.treatment_time]
-        self.datapost = data[data.index > self.treatment_time]
+        self.datapre = data[data.index < self.treatment_time]
+        self.datapost = data[data.index >= self.treatment_time]
 
         self.formula = formula
 
diff --git a/causalpy/skl_experiments.py b/causalpy/skl_experiments.py
index 9db34736..4ec5db65 100644
--- a/causalpy/skl_experiments.py
+++ b/causalpy/skl_experiments.py
@@ -74,8 +74,8 @@ def __init__(
         super().__init__(model=model, **kwargs)
         self.treatment_time = treatment_time
         # split data in to pre and post intervention
-        self.datapre = data[data.index <= self.treatment_time]
-        self.datapost = data[data.index > self.treatment_time]
+        self.datapre = data[data.index < self.treatment_time]
+        self.datapost = data[data.index >= self.treatment_time]
 
         self.formula = formula