diff --git a/src/delta_barth/analysis/forecast.py b/src/delta_barth/analysis/forecast.py
index 55e42ac..21bb096 100644
--- a/src/delta_barth/analysis/forecast.py
+++ b/src/delta_barth/analysis/forecast.py
@@ -255,7 +255,7 @@ def _process_sales(
     # print("dates: ", dates)
     # ?? --- new: use monthly basis for time windows
     # baseline: 3 years - 36 months
-    starting_date = datetime.datetime.now() - relativedelta(months=12)
+    starting_date = datetime.datetime.now() - relativedelta(months=36)
     # starting_date = dates.max() - relativedelta(months=36)
     start_index = next(
         (i for i, date in enumerate(dates) if date >= starting_date), len(dates) - 1