diff --git a/drees.py b/drees.py
index 7847fa2..40a9ee9 100644
--- a/drees.py
+++ b/drees.py
@@ -547,6 +547,13 @@ def plot_bar_vaccine_status_distribution_by_age_field(
     )
 
 
+def check_timestep(np_date: np.ndarray):
+    # get the difference between each element (return timedelta64 array)
+    np_diff = np.diff(np_date)
+    # check if all timestep are equals
+    assert np.all(np_diff == np_diff[0]), "some timesteps missing !"
+
+
 def get_age_vac_args() -> List[Tuple[AgeGroup, VacStatus]]:
     """
     build pool age and vac status arguments
@@ -669,6 +676,7 @@ if __name__ == "__main__":
     np_data, np_date = get_np_data(dic_data)
 
     lst_analyse_data = analyse(np_data)
+    check_timestep(np_date)
 
     if not args.no_plot:
         os.makedirs(OUTPUT_REPOSITORY, exist_ok=True)