diff --git a/DIRECTORY.md b/DIRECTORY.md
index 315810f062..3793104e27 100644
--- a/DIRECTORY.md
+++ b/DIRECTORY.md
@@ -299,6 +299,7 @@
   * [FormatPhoneNumber](String/FormatPhoneNumber.js)
   * [GenerateGUID](String/GenerateGUID.js)
   * [HammingDistance](String/HammingDistance.js)
+  * [IsPalindrome](String/IsPalindrome.js)
   * [KMPPatternSearching](String/KMPPatternSearching.js)
   * [LevenshteinDistance](String/LevenshteinDistance.js)
   * [Lower](String/Lower.js)
diff --git a/String/IsPalindrome.js b/String/IsPalindrome.js
index 27dca7151f..60c1c313a4 100644
--- a/String/IsPalindrome.js
+++ b/String/IsPalindrome.js
@@ -10,7 +10,8 @@
   * Big-O Analysis
       * Time Complexity
         - O(N) on average and worst case scenario as input is traversed in linear fashion
-        - O(N) on best case scenario, even when input has length of 1, because toString() method takes O(N)
+        - O(1) on best case scenario if the input already is a string (otherwise toString() method takes O(N))
+               and the first & last characters don't match, triggering an early return
       * Space Complexity
         - O(1)
 */