diff --git a/app.py b/app.py
index 8e7360d..a70e85a 100644
--- a/app.py
+++ b/app.py
@@ -91,7 +91,7 @@ def generate_report(user_id, begin_date, end_date):
         timestamp = parse_iso_datetime(row["ts"])
         if timestamp < begin_dt or timestamp > end_dt:
             continue
-        delta = row["ts"] - timestamp
+        delta = end_dt - timestamp
         if row["paid"]:
             paid_seconds += delta.total_seconds()
         else: