diff --git a/docs/05.PORT-API.md b/docs/05.PORT-API.md
index 41c72a3252..2b503ef3d5 100644
--- a/docs/05.PORT-API.md
+++ b/docs/05.PORT-API.md
@@ -76,27 +76,34 @@ void jerry_port_log (jerry_log_level_t level, const char *fmt, ...);
 
 ```c
 /**
- * Jerry time zone structure
- */
-typedef struct
-{
-  int offset;                /**< minutes from west */
-  int daylight_saving_time;  /**< daylight saving time (1 - DST applies, 0 - not on DST) */
-} jerry_time_zone_t;
-
-/**
- * Get timezone and daylight saving data
+ * Get local time zone adjustment, in milliseconds, for the given timestamp.
+ * The timestamp can be specified in either UTC or local time, depending on
+ * the value of is_utc. Adding the value returned from this function to
+ * a timestamp in UTC time should result in local time for the current time
+ * zone.
+ *
+ * Ideally, this function should satisfy the stipulations applied to LocalTZA
+ * in section 20.3.1.7 of the ECMAScript version 9.0 spec.
+ *
+ * See Also:
+ *          ECMA-262 v9, 20.3.1.7
  *
  * Note:
  *      This port function is called by jerry-core when
  *      CONFIG_DISABLE_DATE_BUILTIN is _not_ defined. Otherwise this function is
  *      not used.
  *
- * @param[out] tz_p time zone structure to fill.
- * @return true  - if success
- *         false - otherwise
+ * @param unix_ms The unix timestamp we want an offset for, given in
+ *                millisecond precision (could be now, in the future,
+ *                or in the past)
+ * @param is_utc Is the given timestamp in UTC time? If false, it is in local
+ *               time.
+ *
+ * @return milliseconds between local time and UTC for the given timestamp,
+ *         if available
+ *.        0 if not available / we are in UTC.
  */
-bool jerry_port_get_time_zone (jerry_time_zone_t *tz_p);
+double jerry_port_get_local_time_zone_adjustment (double unix_ms, bool is_utc);
 
 /**
  * Get system time
@@ -198,27 +205,21 @@ jerry_port_log (jerry_log_level_t level, /**< log level */
 #include "jerryscript-port.h"
 
 /**
- * Default implementation of jerry_port_get_time_zone.
+ * Default implementation of jerry_port_get_local_time_zone_adjustment.
  */
-bool jerry_port_get_time_zone (jerry_time_zone_t *tz_p)
+double jerry_port_get_local_time_zone_adjustment (double unix_ms, /**< ms since unix epoch */
+                                                  bool is_utc)    /**< is the time above in utc? */
 {
-  struct timeval tv;
-  struct timezone tz;
-
-  /* gettimeofday may not fill tz, so zero-initializing */
-  tz.tz_minuteswest = 0;
-  tz.tz_dsttime = 0;
-
-  if (gettimeofday (&tv, &tz) != 0)
+  struct tm tm;
+  time_t now = (time_t) (unix_ms / 1000);
+  localtime_r (&now, &tm);
+  if (!is_utc)
   {
-    return false;
+    now -= tm.tm_gmtoff;
+    localtime_r (&now, &tm);
   }
-
-  tz_p->offset = tz.tz_minuteswest;
-  tz_p->daylight_saving_time = tz.tz_dsttime > 0 ? 1 : 0;
-
-  return true;
-} /* jerry_port_get_time_zone */
+  return ((double) tm.tm_gmtoff) * 1000;
+} /* jerry_port_get_local_time_zone_adjustment */
 
 /**
  * Default implementation of jerry_port_get_current_time.
diff --git a/jerry-core/ecma/builtin-objects/ecma-builtin-date-prototype.c b/jerry-core/ecma/builtin-objects/ecma-builtin-date-prototype.c
index 4cba274628..454dafa981 100644
--- a/jerry-core/ecma/builtin-objects/ecma-builtin-date-prototype.c
+++ b/jerry-core/ecma/builtin-objects/ecma-builtin-date-prototype.c
@@ -600,7 +600,7 @@ ecma_builtin_date_prototype_dispatch_routine (uint16_t builtin_routine_id, /**<
 
     if (!BUILTIN_DATE_FUNCTION_IS_UTC (builtin_routine_id))
     {
-      this_num += ecma_date_local_time_zone (this_num);
+      this_num += ecma_date_local_time_zone_adjustment (this_num);
     }
 
     if (builtin_routine_id <= ECMA_DATE_PROTOTYPE_GET_UTC_TIMEZONE_OFFSET)
diff --git a/jerry-core/ecma/builtin-objects/ecma-builtin-helpers-date.c b/jerry-core/ecma/builtin-objects/ecma-builtin-helpers-date.c
index 084b0ff479..32476a33a5 100644
--- a/jerry-core/ecma/builtin-objects/ecma-builtin-helpers-date.c
+++ b/jerry-core/ecma/builtin-objects/ecma-builtin-helpers-date.c
@@ -302,64 +302,22 @@ ecma_date_week_day (ecma_number_t time) /**< time value */
 } /* ecma_date_week_day */
 
 /**
- * Helper function to get local time zone adjustment.
- *
- * See also:
- *          ECMA-262 v5, 15.9.1.7
- *
- * @return local time zone adjustment
- */
-static inline ecma_number_t JERRY_ATTR_ALWAYS_INLINE
-ecma_date_local_tza (jerry_time_zone_t *tz) /**< time zone information */
-{
-  return tz->offset * -ECMA_DATE_MS_PER_MINUTE;
-} /* ecma_date_local_tza */
-
-/**
- * Helper function to get the daylight saving time adjustment.
- *
- * See also:
- *          ECMA-262 v5, 15.9.1.8
- *
- * @return daylight saving time adjustment
- */
-static inline ecma_number_t JERRY_ATTR_ALWAYS_INLINE
-ecma_date_daylight_saving_ta (jerry_time_zone_t *tz, /**< time zone information */
-                              ecma_number_t time) /**< time value */
-{
-  JERRY_ASSERT (!ecma_number_is_nan (time));
-
-  /*
-   * TODO: Fix daylight saving calculation.
-   *       https://github.com/jerryscript-project/jerryscript/issues/1661
-   */
-  return tz->daylight_saving_time * ECMA_DATE_MS_PER_HOUR;
-} /* ecma_date_daylight_saving_ta */
-
-/**
- * Helper function to get local time from UTC.
+ * Helper function to get the local time zone offset at a given UTC timestamp.
+ * You can add this number to the given UTC timestamp to get local time.
  *
  * See also:
  *          ECMA-262 v5, 15.9.1.9
  *
- * @return local time
+ * @return local time zone adjustment
  */
 inline ecma_number_t JERRY_ATTR_ALWAYS_INLINE
-ecma_date_local_time_zone (ecma_number_t time) /**< time value */
+ecma_date_local_time_zone_adjustment (ecma_number_t time) /**< time value */
 {
-  jerry_time_zone_t tz;
-
-  if (ecma_number_is_nan (time)
-      || !jerry_port_get_time_zone (&tz))
-  {
-    return ecma_number_make_nan ();
-  }
-
-  return ecma_date_local_tza (&tz) + ecma_date_daylight_saving_ta (&tz, time);
-} /* ecma_date_local_time_zone */
+  return jerry_port_get_local_time_zone_adjustment (time, true);
+} /* ecma_date_local_time_zone_adjustment */
 
 /**
- * Helper function to get utc from local time.
+ * Helper function to get utc time from local time.
  *
  * See also:
  *          ECMA-262 v5, 15.9.1.9
@@ -369,16 +327,7 @@ ecma_date_local_time_zone (ecma_number_t time) /**< time value */
 ecma_number_t
 ecma_date_utc (ecma_number_t time) /**< time value */
 {
-  jerry_time_zone_t tz;
-
-  if (ecma_number_is_nan (time)
-      || !jerry_port_get_time_zone (&tz))
-  {
-    return ecma_number_make_nan ();
-  }
-
-  ecma_number_t simple_utc_time = time - ecma_date_local_tza (&tz);
-  return simple_utc_time - ecma_date_daylight_saving_ta (&tz, simple_utc_time);
+  return time - jerry_port_get_local_time_zone_adjustment (time, false);
 } /* ecma_date_utc */
 
 /**
@@ -615,7 +564,7 @@ ecma_date_timezone_offset (ecma_number_t time) /**< time value */
 {
   JERRY_ASSERT (!ecma_number_is_nan (time));
 
-  return (-ecma_date_local_time_zone (time)) / ECMA_DATE_MS_PER_MINUTE;
+  return (-ecma_date_local_time_zone_adjustment (time)) / ECMA_DATE_MS_PER_MINUTE;
 } /* ecma_date_timezone_offset */
 
 /**
@@ -724,7 +673,7 @@ ecma_date_to_string_format (ecma_number_t datetime_number, /**< datetime */
       }
       case LIT_CHAR_LOWERCASE_Z: /* Time zone minutes part. */
       {
-        int32_t time_zone = (int32_t) ecma_date_local_time_zone (datetime_number);
+        int32_t time_zone = (int32_t) ecma_date_local_time_zone_adjustment (datetime_number);
 
         if (time_zone >= 0)
         {
@@ -744,7 +693,7 @@ ecma_date_to_string_format (ecma_number_t datetime_number, /**< datetime */
       {
         JERRY_ASSERT (*format_p == LIT_CHAR_UPPERCASE_Z); /* Time zone seconds part. */
 
-        int32_t time_zone = (int32_t) ecma_date_local_time_zone (datetime_number);
+        int32_t time_zone = (int32_t) ecma_date_local_time_zone_adjustment (datetime_number);
 
         if (time_zone < 0)
         {
@@ -805,7 +754,7 @@ ecma_date_to_string_format (ecma_number_t datetime_number, /**< datetime */
 ecma_value_t
 ecma_date_value_to_string (ecma_number_t datetime_number) /**< datetime */
 {
-  datetime_number += ecma_date_local_time_zone (datetime_number);
+  datetime_number += ecma_date_local_time_zone_adjustment (datetime_number);
   return ecma_date_to_string_format (datetime_number, "$W $M $D $Y $h:$m:$s GMT$z:$Z");
 } /* ecma_date_value_to_string */
 
diff --git a/jerry-core/ecma/builtin-objects/ecma-builtin-helpers.h b/jerry-core/ecma/builtin-objects/ecma-builtin-helpers.h
index 68df529952..83f867eb3c 100644
--- a/jerry-core/ecma/builtin-objects/ecma-builtin-helpers.h
+++ b/jerry-core/ecma/builtin-objects/ecma-builtin-helpers.h
@@ -100,7 +100,7 @@ ecma_number_t ecma_date_year_from_time (ecma_number_t time);
 ecma_number_t ecma_date_month_from_time (ecma_number_t time);
 ecma_number_t ecma_date_date_from_time (ecma_number_t time);
 ecma_number_t ecma_date_week_day (ecma_number_t time);
-ecma_number_t ecma_date_local_time_zone (ecma_number_t time);
+ecma_number_t ecma_date_local_time_zone_adjustment (ecma_number_t time);
 ecma_number_t ecma_date_utc (ecma_number_t time);
 ecma_number_t ecma_date_hour_from_time (ecma_number_t time);
 ecma_number_t ecma_date_min_from_time (ecma_number_t time);
diff --git a/jerry-core/include/jerryscript-port.h b/jerry-core/include/jerryscript-port.h
index 59e4b61d29..3787f6c5b2 100644
--- a/jerry-core/include/jerryscript-port.h
+++ b/jerry-core/include/jerryscript-port.h
@@ -111,27 +111,34 @@ void JERRY_ATTR_FORMAT (printf, 2, 3) jerry_port_log (jerry_log_level_t level, c
  */
 
 /**
- * Jerry time zone structure
- */
-typedef struct
-{
-  int offset;                /**< minutes from west */
-  int daylight_saving_time;  /**< daylight saving time (1 - DST applies, 0 - not on DST) */
-} jerry_time_zone_t;
-
-/**
- * Get timezone and daylight saving data
+ * Get local time zone adjustment, in milliseconds, for the given timestamp.
+ * The timestamp can be specified in either UTC or local time, depending on
+ * the value of is_utc. Adding the value returned from this function to
+ * a timestamp in UTC time should result in local time for the current time
+ * zone.
+ *
+ * Ideally, this function should satisfy the stipulations applied to LocalTZA
+ * in section 20.3.1.7 of the ECMAScript version 9.0 spec.
+ *
+ * See Also:
+ *          ECMA-262 v9, 20.3.1.7
  *
  * Note:
  *      This port function is called by jerry-core when
  *      CONFIG_DISABLE_DATE_BUILTIN is _not_ defined. Otherwise this function is
  *      not used.
  *
- * @param[out] tz_p time zone structure to fill.
- * @return true  - if success
- *         false - otherwise
+ * @param unix_ms The unix timestamp we want an offset for, given in
+ *                millisecond precision (could be now, in the future,
+ *                or in the past)
+ * @param is_utc Is the given timestamp in UTC time? If false, it is in local
+ *               time.
+ *
+ * @return milliseconds between local time and UTC for the given timestamp,
+ *         if available
+ *.        0 if not available / we are in UTC.
  */
-bool jerry_port_get_time_zone (jerry_time_zone_t *tz_p);
+double jerry_port_get_local_time_zone_adjustment (double unix_ms, bool is_utc);
 
 /**
  * Get system time
diff --git a/jerry-port/default/CMakeLists.txt b/jerry-port/default/CMakeLists.txt
index e388dc9936..025965a24d 100644
--- a/jerry-port/default/CMakeLists.txt
+++ b/jerry-port/default/CMakeLists.txt
@@ -26,6 +26,12 @@ file(GLOB SOURCE_PORT_DEFAULT *.c)
 # (should only be necessary if we used compiler default libc but not checking that)
 set(DEFINES_PORT_DEFAULT _BSD_SOURCE _DEFAULT_SOURCE)
 
+INCLUDE (CheckStructHasMember)
+CHECK_STRUCT_HAS_MEMBER ("struct tm" tm_gmtoff time.h HAVE_TM_GMTOFF)
+if(HAVE_TM_GMTOFF)
+  set(DEFINES_PORT_DEFAULT ${DEFINES_PORT_DEFAULT} HAVE_TM_GMTOFF)
+endif()
+
 # Sleep function availability check
 INCLUDE (CheckIncludeFiles)
 CHECK_INCLUDE_FILES (time.h HAVE_TIME_H)
diff --git a/jerry-port/default/default-date.c b/jerry-port/default/default-date.c
index 837ef7d80e..e2db60b3e8 100644
--- a/jerry-port/default/default-date.c
+++ b/jerry-port/default/default-date.c
@@ -13,6 +13,9 @@
  * limitations under the License.
  */
 
+#ifdef HAVE_TM_GMTOFF
+#include <time.h>
+#endif
 #ifdef __GNUC__
 #include <sys/time.h>
 #endif
@@ -21,33 +24,32 @@
 #include "jerryscript-port-default.h"
 
 /**
- * Default implementation of jerry_port_get_time_zone. Uses 'gettimeofday' if
- * available on the system, does nothing otherwise.
+ * Default implementation of jerry_port_get_local_time_zone_adjustment. Uses the 'tm_gmtoff' field
+ * of 'struct tm' (a GNU extension) filled by 'localtime_r' if available on the
+ * system, does nothing otherwise.
  *
- * @return true - if 'gettimeofday' is available and executed successfully,
- *         false - otherwise.
+ * @return offset between UTC and local time at the given unix timestamp, if
+ *         available. Otherwise, returns 0, assuming UTC time.
  */
-bool jerry_port_get_time_zone (jerry_time_zone_t *tz_p) /**< [out] time zone structure to fill */
+double jerry_port_get_local_time_zone_adjustment (double unix_ms,  /**< ms since unix epoch */
+                                                  bool is_utc)  /**< is the time above in UTC? */
 {
-#ifdef __GNUC__
-  struct timeval tv;
-  struct timezone tz;
-
-  /* gettimeofday may not fill tz, so zero-initializing */
-  tz.tz_minuteswest = 0;
-  tz.tz_dsttime = 0;
-
-  if (gettimeofday (&tv, &tz) == 0)
+#ifdef HAVE_TM_GMTOFF
+  struct tm tm;
+  time_t now = (time_t) (unix_ms / 1000);
+  localtime_r (&now, &tm);
+  if (!is_utc)
   {
-    tz_p->offset = tz.tz_minuteswest;
-    tz_p->daylight_saving_time = tz.tz_dsttime > 0 ? 1 : 0;
-
-    return true;
+    now -= tm.tm_gmtoff;
+    localtime_r (&now, &tm);
   }
-#endif /* __GNUC__ */
-
-  return false;
-} /* jerry_port_get_time_zone */
+  return ((double) tm.tm_gmtoff) * 1000;
+#else
+  (void) unix_ms;
+  (void) is_utc;
+  return 0.0;
+#endif /* HAVE_TM_GMTOFF */
+} /* jerry_port_get_local_time_zone_adjustment */
 
 /**
  * Default implementation of jerry_port_get_current_time. Uses 'gettimeofday' if
diff --git a/targets/curie_bsp/source/curie-bsp-port.c b/targets/curie_bsp/source/curie-bsp-port.c
index 97cb896c42..1def05e2ec 100644
--- a/targets/curie_bsp/source/curie-bsp-port.c
+++ b/targets/curie_bsp/source/curie-bsp-port.c
@@ -52,16 +52,13 @@ void jerry_port_fatal (jerry_fatal_code_t code)
 } /* jerry_port_fatal */
 
 /**
- * Curie BSP implementation of jerry_port_get_time_zone.
+ * Curie BSP implementation of jerry_port_get_local_time_zone_adjustment.
  */
-bool jerry_port_get_time_zone (jerry_time_zone_t *tz_p)
+double jerry_port_get_local_time_zone_adjustment (double unix_ms, bool is_utc)
 {
   //EMPTY implementation
-  tz_p->offset = 0;
-  tz_p->daylight_saving_time = 0;
-
-  return true;
-} /* jerry_port_get_time_zone */
+  return 0;
+} /* jerry_port_get_local_time_zone_adjustment */
 
 /**
  * Curie BSP implementation of jerry_port_get_current_time.
diff --git a/targets/esp8266/user/jerry_port.c b/targets/esp8266/user/jerry_port.c
index 7ba25e43ad..f4d5876973 100644
--- a/targets/esp8266/user/jerry_port.c
+++ b/targets/esp8266/user/jerry_port.c
@@ -61,16 +61,13 @@ jerry_port_get_current_time (void)
 } /* jerry_port_get_current_time */
 
 /**
- * Dummy function to get the time zone.
+ * Dummy function to get the time zone adjustment.
  *
- * @return true
+ * @return 0
  */
-bool
-jerry_port_get_time_zone (jerry_time_zone_t *tz_p)
+double
+jerry_port_get_local_time_zone_adjustment (double unix_ms, bool is_utc)
 {
   /* We live in UTC. */
-  tz_p->offset = 0;
-  tz_p->daylight_saving_time = 0;
-
-  return true;
-} /* jerry_port_get_time_zone */
+  return 0;
+} /* jerry_port_get_local_time_zone_adjustment */
diff --git a/targets/mbedos5/source/jerry_port_mbed.c b/targets/mbedos5/source/jerry_port_mbed.c
index 3e225b0136..3572647157 100644
--- a/targets/mbedos5/source/jerry_port_mbed.c
+++ b/targets/mbedos5/source/jerry_port_mbed.c
@@ -46,17 +46,15 @@ jerry_port_log (jerry_log_level_t level, /**< log level */
 #endif /* JSMBED_OVERRIDE_JERRY_PORT_LOG */
 
 /**
- * Implementation of jerry_port_get_time_zone.
+ * Implementation of jerry_port_get_local_time_zone_adjustment.
  *
- * @return true - if success
+ * @return 0, as we live in UTC.
  */
-bool
-jerry_port_get_time_zone (jerry_time_zone_t *tz_p) /**< timezone pointer */
+double
+jerry_port_get_local_time_zone_adjustment (double unix_ms, bool is_utc)
 {
-  tz_p->offset = 0;
-  tz_p->daylight_saving_time = 0;
-  return true;
-} /* jerry_port_get_time_zone */
+  return 0;
+} /* jerry_port_get_local_time_zone_adjustment */
 
 /**
  * Implementation of jerry_port_get_current_time.
diff --git a/targets/nuttx-stm32f4/jerry_main.c b/targets/nuttx-stm32f4/jerry_main.c
index ef6a63c798..61419b99b9 100644
--- a/targets/nuttx-stm32f4/jerry_main.c
+++ b/targets/nuttx-stm32f4/jerry_main.c
@@ -492,19 +492,16 @@ jerry_port_log (jerry_log_level_t level, /**< log level */
 } /* jerry_port_log */
 
 /**
- * Dummy function to get the time zone.
+ * Dummy function to get the time zone adjustment.
  *
- * @return true
+ * @return 0
  */
-bool
-jerry_port_get_time_zone (jerry_time_zone_t *tz_p)
+double
+jerry_port_get_local_time_zone_adjustment (double unix_ms, bool is_utc)
 {
   /* We live in UTC. */
-  tz_p->offset = 0;
-  tz_p->daylight_saving_time = 0;
-
-  return true;
-} /* jerry_port_get_time_zone */
+  return 0;
+} /* jerry_port_get_local_time_zone_adjustment */
 
 /**
  * Dummy function to get the current time.
diff --git a/targets/tizenrt-artik053/apps/jerryscript/jerry_main.c b/targets/tizenrt-artik053/apps/jerryscript/jerry_main.c
index ce8cbe23ae..2774c58193 100644
--- a/targets/tizenrt-artik053/apps/jerryscript/jerry_main.c
+++ b/targets/tizenrt-artik053/apps/jerryscript/jerry_main.c
@@ -474,19 +474,16 @@ jerry_port_log (jerry_log_level_t level, /**< log level */
 } /* jerry_port_log */
 
 /**
- * Dummy function to get the time zone.
+ * Dummy function to get the time zone adjustment.
  *
- * @return true
+ * @return 0
  */
-bool
-jerry_port_get_time_zone (jerry_time_zone_t *tz_p)
+double
+jerry_port_get_local_time_zone_adjustment (double unix_ms, bool is_utc)
 {
   /* We live in UTC. */
-  tz_p->offset = 0;
-  tz_p->daylight_saving_time = 0;
-
-  return true;
-} /* jerry_port_get_time_zone */
+  return 0;
+} /* jerry_port_get_local_time_zone_adjustment */
 
 /**
  * Dummy function to get the current time.
diff --git a/targets/zephyr/src/jerry-port.c b/targets/zephyr/src/jerry-port.c
index b1eb9dcb67..5a129d8fbe 100644
--- a/targets/zephyr/src/jerry-port.c
+++ b/targets/zephyr/src/jerry-port.c
@@ -59,19 +59,16 @@ jerry_port_get_current_time (void)
 } /* jerry_port_get_current_time */
 
 /**
- * Dummy function to get the time zone.
+ * Dummy function to get the time zone adjustment.
  *
- * @return true
+ * @return 0
  */
-bool
-jerry_port_get_time_zone (jerry_time_zone_t *tz_p)
+double
+jerry_port_get_local_time_zone_adjustment (double unix_ms, bool is_utc)
 {
   /* We live in UTC. */
-  tz_p->offset = 0;
-  tz_p->daylight_saving_time = 0;
-
-  return true;
-} /* jerry_port_get_time_zone */
+  return 0;
+} /* jerry_port_get_local_time_zone_adjustment */
 
 /**
  * Provide the implementation of jerryx_port_handler_print_char.