diff --git a/form.php b/form.php
index 78150e2..dc6ddfc 100644
--- a/form.php
+++ b/form.php
@@ -301,6 +301,24 @@ class form
     }
     return $errors;
   }
+
+  /** Convert Date received in one format to another.
+    * If the provided string is not corresponding to the format, don't change
+    * anything.
+    * Format used http://php.net/manual/en/datetime.createfromformat.php
+    * @param string $inputDate
+    * @param string $inputFormat
+    * @param string $outputFormat
+    * @return string
+    */
+  public function convertDate ($inputDate, $inputFormat, $outputFormat)
+  {
+    $date = DateTime::CreateFromFormat ($inputFormat, $inputDate);
+    $errors = $date->getLastErrors();
+    if ($errors["warning_count"] > 0 || $errors["error_count"] > 0)
+      return $inputDate;
+    return $date->format ($outputFormat);
+  }
 }
 
 /** the definition of a formfield */