diff --git a/src/wp-includes/formatting.php b/src/wp-includes/formatting.php
index aef9c5555c..a07a020629 100644
--- a/src/wp-includes/formatting.php
+++ b/src/wp-includes/formatting.php
@@ -2335,8 +2335,9 @@ function sanitize_email( $email ) {
  * @return string Human readable time difference.
  */
 function human_time_diff( $from, $to = '' ) {
-	if ( empty( $to ) )
+	if ( empty( $to ) ) {
 		$to = time();
+	}
 
 	$diff = (int) abs( $to - $from );
 
@@ -2373,7 +2374,17 @@ function human_time_diff( $from, $to = '' ) {
 		$since = sprintf( _n( '%s year', '%s years', $years ), $years );
 	}
 
-	return $since;
+	/**
+	 * Filter the human readable difference between two timestamps.
+	 *
+	 * @since 4.0.0
+	 *
+	 * @param string $since The difference in human readable text.
+	 * @param int    $diff  The difference in seconds.
+	 * @param int    $from  Unix timestamp from which the difference begins.
+	 * @param int    $to    Unix timestamp to end the time difference.
+	 */
+	return apply_filters( 'human_time_diff', $since, $diff, $from, $to );
 }
 
 /**