diff --git a/zfs_smart_snapshot/main.py b/zfs_smart_snapshot/main.py
index 74dff97..504a513 100644
--- a/zfs_smart_snapshot/main.py
+++ b/zfs_smart_snapshot/main.py
@@ -13,7 +13,7 @@ def keep_time(now, snapshots, convert, delta, count):
     keep = set()
     if count < 1:
         return keep
-    start = convert(now) - delta*(count-1)
+    start = convert(now) - delta*count
     for snapshot in snapshots:
         snapdate = datetime.strptime(snapshot, 'zfs-smart-snap-%Y-%m-%d-%H%M').replace(tzinfo=timezone.utc)
         if snapdate >= start: