diff --git a/src/sortedcontainers/sortedlist.py b/src/sortedcontainers/sortedlist.py
index aecf787..54e04de 100644
--- a/src/sortedcontainers/sortedlist.py
+++ b/src/sortedcontainers/sortedlist.py
@@ -1076,7 +1076,9 @@ def __len__(self):
         """Return the size of the sorted list.
 
         ``sl.__len__()`` <==> ``len(sl)``
-
+        
+        Runtime complexity: `O(1)`
+        
         :return: size of sorted list
 
         """
diff --git a/src/sortedcontainers/sortedset.py b/src/sortedcontainers/sortedset.py
index f2416bf..2071d63 100644
--- a/src/sortedcontainers/sortedset.py
+++ b/src/sortedcontainers/sortedset.py
@@ -289,7 +289,9 @@ def __len__(self):
         """Return the size of the sorted set.
 
         ``ss.__len__()`` <==> ``len(ss)``
-
+        
+        Runtime complexity: `O(1)`
+        
         :return: size of sorted set
 
         """