diff -u b/core/modules/migrate/src/Plugin/migrate/process/FormatDate.php b/core/modules/migrate/src/Plugin/migrate/process/FormatDate.php
--- b/core/modules/migrate/src/Plugin/migrate/process/FormatDate.php
+++ b/core/modules/migrate/src/Plugin/migrate/process/FormatDate.php
@@ -25,6 +25,18 @@
  *   DateTimePlus::__construct().
  * - settings: keyed array of settings, see DateTimePlus::__construct().
  *
+ * Configuration keys from_timezone and to_timezone are both optional. Possible
+ * input variants:
+ * - Both from_timezone and to_timezone are empty. Date will not be converted
+ *   and be treated as date in default timezone.
+ * - Only from_timezone is set. Date will be converted from timezone specified
+ *   in from_timezone key to the default timezone.
+ * - Only to_timezone is set. Date will be converted from the default timezone
+ *   to the timezone specified in to_timezone key.
+ * - Both from_timezone and to_timezone are set. Date will be converted from
+ *   timezone specified in from_timezone key to the timezone specified in
+ *   to_timezone key.
+ *
  * Examples:
  *
  * Example usage for date only fields (DATETIME_DATE_STORAGE_FORMAT):
@@ -100,19 +112,22 @@
     $toFormat = $this->configuration['to_format'];
     if (isset($this->configuration['timezone'])) {
       @trigger_error('Configuration key "timezone" is deprecated in 8.4.0 and will be removed before Drupal 9.0.0, use "from_timezone" and "to_timezone" instead. See https://www.drupal.org/node/2885746', E_USER_DEPRECATED);
+      $from_timezone = $this->configuration['timezone'];
+      $to_timezone = NULL;
+    }
+    else {
+      $system_timezone = date_default_timezone_get();
+      $default_timezone = !empty($system_timezone) ? $system_timezone : 'UTC';
+      $from_timezone = isset($this->configuration['from_timezone']) ? $this->configuration['from_timezone'] : $default_timezone;
+      $to_timezone = isset($this->configuration['to_timezone']) ? $this->configuration['to_timezone'] : $default_timezone;
     }
-    $timezone = isset($this->configuration['timezone']) ? $this->configuration['timezone'] : NULL;
-    $from_timezone = isset($this->configuration['from_timezone']) ? $this->configuration['from_timezone'] : $timezone;
-    $to_timezone = isset($this->configuration['to_timezone']) ? $this->configuration['to_timezone'] : NULL;
     $settings = isset($this->configuration['settings']) ? $this->configuration['settings'] : [];
 
     // Attempts to transform the supplied date using the defined input format.
     // DateTimePlus::createFromFormat can throw exceptions, so we need to
     // explicitly check for problems.
     try {
-      $date = DateTimePlus::createFromFormat($fromFormat, $value, $from_timezone, $settings);
-      //$date->setTimezone(new \DateTimeZone($from_timezone));
-      $transformed = $date->format($toFormat, ['timezone' => $to_timezone]);
+      $transformed = DateTimePlus::createFromFormat($fromFormat, $value, $from_timezone, $settings)->format($toFormat, ['timezone' => $to_timezone]);
     }
     catch (\InvalidArgumentException $e) {
       throw new MigrateException(sprintf('Format date plugin could not transform "%s" using the format "%s". Error: %s', $value, $fromFormat, $e->getMessage()), $e->getCode(), $e);
diff -u b/core/modules/migrate/tests/src/Unit/process/FormatDateTest.php b/core/modules/migrate/tests/src/Unit/process/FormatDateTest.php
--- b/core/modules/migrate/tests/src/Unit/process/FormatDateTest.php
+++ b/core/modules/migrate/tests/src/Unit/process/FormatDateTest.php
@@ -84,7 +84,7 @@
     $this->plugin = new FormatDate($configuration, 'test_format_date', []);
     $actual = $this->plugin->transform('2004-12-19T10:19:42-0600', $this->migrateExecutable, $this->row, 'field_date');
 
-    $this->assertEquals('2004-12-19T10:19:42-06:00 America/Managua', $actual);
+    $this->assertEquals('2004-12-19T10:19:42-06:00 -06:00', $actual);
   }
 
   /**
@@ -127,10 +127,10 @@
       'datetime_datetime' => [
         'configuration' => [
           'from_format' => 'm/d/Y H:i:s',
-          'to_format' => 'Y-m-d\TH:i:s',
+          'to_format' => 'Y-m-d\TH:i:s e',
         ],
         'value' => '01/05/1955 10:43:22',
-        'expected' => '1955-01-05T10:43:22',
+        'expected' => '1955-01-05T10:43:22 Australia/Sydney',
       ],
       'empty_values' => [
         'configuration' => [
@@ -143,30 +143,34 @@
       'timezone_from_to' => [
         'configuration' => [
           'from_format' => 'Y-m-d H:i:s',
-          'to_format' => 'Y-m-d H:i:s',
+          'to_format' => 'Y-m-d H:i:s e',
           'from_timezone' => 'America/Managua',
           'to_timezone' => 'UTC',
         ],
         'value' => '2004-12-19 10:19:42',
-        'expected' => '2004-12-19 16:19:42',
+        'expected' => '2004-12-19 16:19:42 UTC',
       ],
       'timezone_from' => [
         'configuration' => [
           'from_format' => 'Y-m-d h:i:s',
-          'to_format' => 'Y-m-d h:i:s',
+          'to_format' => 'Y-m-d h:i:s e',
           'from_timezone' => 'America/Managua',
         ],
         'value' => '2004-11-19 10:25:33',
-        'expected' => '2004-11-19 10:25:33',
+        // Unit tests use Australia/Sydney timezone, so date value will be
+        // converted from America/Managua to Australia/Sydney timezone.
+        'expected' => '2004-11-20 03:25:33 Australia/Sydney',
       ],
       'timezone_to' => [
         'configuration' => [
           'from_format' => 'Y-m-d H:i:s',
-          'to_format' => 'Y-m-d H:i:s',
+          'to_format' => 'Y-m-d H:i:s e',
           'to_timezone' => 'America/Managua',
         ],
         'value' => '2004-12-19 10:19:42',
-        'expected' => '2004-12-19 04:19:42',
+        // Unit tests use Australia/Sydney timezone, so date value will be
+        // converted from Australia/Sydney to America/Managua timezone.
+        'expected' => '2004-12-18 17:19:42 America/Managua',
       ],
     ];
   }