diff --git a/src/PhpSpreadsheet/Calculation/TextData/Format.php b/src/PhpSpreadsheet/Calculation/TextData/Format.php
index 67101ca1d..df7cb5637 100644
--- a/src/PhpSpreadsheet/Calculation/TextData/Format.php
+++ b/src/PhpSpreadsheet/Calculation/TextData/Format.php
@@ -124,6 +124,7 @@ class Format
 
         $value = Helpers::extractString($value);
         $format = Helpers::extractString($format);
+        $format = (string) NumberFormat::convertSystemFormats($format);
 
         if (!is_numeric($value) && Date::isDateTimeFormatCode($format)) {
             // @phpstan-ignore-next-line
diff --git a/src/PhpSpreadsheet/Cell/Cell.php b/src/PhpSpreadsheet/Cell/Cell.php
index 987e1a361..4cbdbbe92 100644
--- a/src/PhpSpreadsheet/Cell/Cell.php
+++ b/src/PhpSpreadsheet/Cell/Cell.php
@@ -182,7 +182,7 @@ class Cell implements Stringable
     {
         return (string) NumberFormat::toFormattedString(
             $this->getCalculatedValue(),
-            (string) $this->getStyle()->getNumberFormat()->getFormatCode()
+            (string) $this->getStyle()->getNumberFormat()->getFormatCode(true)
         );
     }
 
diff --git a/src/PhpSpreadsheet/Shared/Date.php b/src/PhpSpreadsheet/Shared/Date.php
index 55fe77c37..ed19534de 100644
--- a/src/PhpSpreadsheet/Shared/Date.php
+++ b/src/PhpSpreadsheet/Shared/Date.php
@@ -411,6 +411,7 @@ class Date
         }
 
         // Switch on formatcode
+        $excelFormatCode = (string) NumberFormat::convertSystemFormats($excelFormatCode);
         if (in_array($excelFormatCode, NumberFormat::DATE_TIME_OR_DATETIME_ARRAY, true)) {
             return $dateWithoutTimeOkay || in_array($excelFormatCode, NumberFormat::TIME_OR_DATETIME_ARRAY);
         }
diff --git a/src/PhpSpreadsheet/Style/NumberFormat.php b/src/PhpSpreadsheet/Style/NumberFormat.php
index 5153d84de..b344da64b 100644
--- a/src/PhpSpreadsheet/Style/NumberFormat.php
+++ b/src/PhpSpreadsheet/Style/NumberFormat.php
@@ -26,10 +26,12 @@ class NumberFormat extends Supervisor
     const FORMAT_DATE_DMMINUS = 'd-m';
     const FORMAT_DATE_MYMINUS = 'm-yy';
     const FORMAT_DATE_XLSX14 = 'mm-dd-yy';
+    const FORMAT_DATE_XLSX14_ACTUAL = 'm/d/yyyy';
     const FORMAT_DATE_XLSX15 = 'd-mmm-yy';
     const FORMAT_DATE_XLSX16 = 'd-mmm';
     const FORMAT_DATE_XLSX17 = 'mmm-yy';
     const FORMAT_DATE_XLSX22 = 'm/d/yy h:mm';
+    const FORMAT_DATE_XLSX22_ACTUAL = 'm/d/yyyy h:mm';
     const FORMAT_DATE_DATETIME = 'd/m/yy h:mm';
     const FORMAT_DATE_TIME1 = 'h:mm AM/PM';
     const FORMAT_DATE_TIME2 = 'h:mm:ss AM/PM';
@@ -40,6 +42,7 @@ class NumberFormat extends Supervisor
     const FORMAT_DATE_TIME7 = 'i:s.S';
     const FORMAT_DATE_TIME8 = 'h:mm:ss;@';
     const FORMAT_DATE_YYYYMMDDSLASH = 'yyyy/mm/dd;@';
+    const FORMAT_DATE_LONG_DATE = 'dddd, mmmm d, yyyy';
 
     const DATE_TIME_OR_DATETIME_ARRAY = [
         self::FORMAT_DATE_YYYYMMDD,
@@ -49,10 +52,12 @@ class NumberFormat extends Supervisor
         self::FORMAT_DATE_DMMINUS,
         self::FORMAT_DATE_MYMINUS,
         self::FORMAT_DATE_XLSX14,
+        self::FORMAT_DATE_XLSX14_ACTUAL,
         self::FORMAT_DATE_XLSX15,
         self::FORMAT_DATE_XLSX16,
         self::FORMAT_DATE_XLSX17,
         self::FORMAT_DATE_XLSX22,
+        self::FORMAT_DATE_XLSX22_ACTUAL,
         self::FORMAT_DATE_DATETIME,
         self::FORMAT_DATE_TIME1,
         self::FORMAT_DATE_TIME2,
@@ -63,6 +68,7 @@ class NumberFormat extends Supervisor
         self::FORMAT_DATE_TIME7,
         self::FORMAT_DATE_TIME8,
         self::FORMAT_DATE_YYYYMMDDSLASH,
+        self::FORMAT_DATE_LONG_DATE,
     ];
     const TIME_OR_DATETIME_ARRAY = [
         self::FORMAT_DATE_XLSX22,
@@ -84,6 +90,21 @@ class NumberFormat extends Supervisor
     const FORMAT_ACCOUNTING_USD = '_("$"* #,##0.00_);_("$"* \(#,##0.00\);_("$"* "-"??_);_(@_)';
     const FORMAT_ACCOUNTING_EUR = '_("€"* #,##0.00_);_("€"* \(#,##0.00\);_("€"* "-"??_);_(@_)';
 
+    const SHORT_DATE_INDEX = 14;
+    const DATE_TIME_INDEX = 22;
+    const FORMAT_SYSDATE_X = '[$-x-sysdate]';
+    const FORMAT_SYSDATE_F800 = '[$-F800]';
+    const FORMAT_SYSTIME_X = '[$-x-systime]';
+    const FORMAT_SYSTIME_F400 = '[$-F400]';
+
+    protected static string $shortDateFormat = self::FORMAT_DATE_XLSX14_ACTUAL;
+
+    protected static string $longDateFormat = self::FORMAT_DATE_LONG_DATE;
+
+    protected static string $dateTimeFormat = self::FORMAT_DATE_XLSX22_ACTUAL;
+
+    protected static string $timeFormat = self::FORMAT_DATE_TIME2;
+
     /**
      * Excel built-in number formats.
      */
@@ -178,16 +199,40 @@ class NumberFormat extends Supervisor
     /**
      * Get Format Code.
      */
-    public function getFormatCode(): ?string
+    public function getFormatCode(bool $extended = false): ?string
     {
         if ($this->isSupervisor) {
-            return $this->getSharedComponent()->getFormatCode();
+            return $this->getSharedComponent()->getFormatCode($extended);
         }
-        if (is_int($this->builtInFormatCode)) {
-            return self::builtInFormatCode($this->builtInFormatCode);
+        $builtin = $this->getBuiltInFormatCode();
+        if (is_int($builtin)) {
+            if ($extended) {
+                if ($builtin === self::SHORT_DATE_INDEX) {
+                    return self::$shortDateFormat;
+                }
+                if ($builtin === self::DATE_TIME_INDEX) {
+                    return self::$dateTimeFormat;
+                }
+            }
+
+            return self::builtInFormatCode($builtin);
         }
 
-        return $this->formatCode;
+        return $extended ? self::convertSystemFormats($this->formatCode) : $this->formatCode;
+    }
+
+    public static function convertSystemFormats(?string $formatCode): ?string
+    {
+        if (is_string($formatCode)) {
+            if (stripos($formatCode, self::FORMAT_SYSDATE_F800) !== false || stripos($formatCode, self::FORMAT_SYSDATE_X) !== false) {
+                return self::$longDateFormat;
+            }
+            if (stripos($formatCode, self::FORMAT_SYSTIME_F400) !== false || stripos($formatCode, self::FORMAT_SYSTIME_X) !== false) {
+                return self::$timeFormat;
+            }
+        }
+
+        return $formatCode;
     }
 
     /**
@@ -290,15 +335,15 @@ class NumberFormat extends Supervisor
             self::$builtInFormats[11] = '0.00E+00';
             self::$builtInFormats[12] = '# ?/?';
             self::$builtInFormats[13] = '# ??/??';
-            self::$builtInFormats[14] = 'm/d/yyyy'; // Despite ECMA 'mm-dd-yy';
-            self::$builtInFormats[15] = 'd-mmm-yy';
+            self::$builtInFormats[14] = self::FORMAT_DATE_XLSX14_ACTUAL; // Despite ECMA 'mm-dd-yy';
+            self::$builtInFormats[15] = self::FORMAT_DATE_XLSX15;
             self::$builtInFormats[16] = 'd-mmm';
             self::$builtInFormats[17] = 'mmm-yy';
             self::$builtInFormats[18] = 'h:mm AM/PM';
             self::$builtInFormats[19] = 'h:mm:ss AM/PM';
             self::$builtInFormats[20] = 'h:mm';
             self::$builtInFormats[21] = 'h:mm:ss';
-            self::$builtInFormats[22] = 'm/d/yyyy h:mm'; // Despite ECMA 'm/d/yy h:mm';
+            self::$builtInFormats[22] = self::FORMAT_DATE_XLSX22_ACTUAL; // Despite ECMA 'm/d/yy h:mm';
 
             self::$builtInFormats[37] = '#,##0_);(#,##0)'; //  Despite ECMA '#,##0 ;(#,##0)';
             self::$builtInFormats[38] = '#,##0_);[Red](#,##0)'; //  Despite ECMA '#,##0 ;[Red](#,##0)';
@@ -427,4 +472,44 @@ class NumberFormat extends Supervisor
 
         return $exportedArray;
     }
+
+    public static function getShortDateFormat(): string
+    {
+        return self::$shortDateFormat;
+    }
+
+    public static function setShortDateFormat(string $shortDateFormat): void
+    {
+        self::$shortDateFormat = $shortDateFormat;
+    }
+
+    public static function getLongDateFormat(): string
+    {
+        return self::$longDateFormat;
+    }
+
+    public static function setLongDateFormat(string $longDateFormat): void
+    {
+        self::$longDateFormat = $longDateFormat;
+    }
+
+    public static function getDateTimeFormat(): string
+    {
+        return self::$dateTimeFormat;
+    }
+
+    public static function setDateTimeFormat(string $dateTimeFormat): void
+    {
+        self::$dateTimeFormat = $dateTimeFormat;
+    }
+
+    public static function getTimeFormat(): string
+    {
+        return self::$timeFormat;
+    }
+
+    public static function setTimeFormat(string $timeFormat): void
+    {
+        self::$timeFormat = $timeFormat;
+    }
 }
diff --git a/src/PhpSpreadsheet/Worksheet/Worksheet.php b/src/PhpSpreadsheet/Worksheet/Worksheet.php
index 2ba3f0818..a6507b94f 100644
--- a/src/PhpSpreadsheet/Worksheet/Worksheet.php
+++ b/src/PhpSpreadsheet/Worksheet/Worksheet.php
@@ -746,7 +746,7 @@ class Worksheet implements IComparable
                         $cellValue = NumberFormat::toFormattedString(
                             $cell->getCalculatedValue(),
                             (string) $this->getParentOrThrow()->getCellXfByIndex($cell->getXfIndex())
-                                ->getNumberFormat()->getFormatCode()
+                                ->getNumberFormat()->getFormatCode(true)
                         );
 
                         if ($cellValue !== null && $cellValue !== '') {
diff --git a/tests/PhpSpreadsheetTests/Style/NumberFormatSystemDateTimeTest.php b/tests/PhpSpreadsheetTests/Style/NumberFormatSystemDateTimeTest.php
new file mode 100644
index 000000000..52799b33e
--- /dev/null
+++ b/tests/PhpSpreadsheetTests/Style/NumberFormatSystemDateTimeTest.php
@@ -0,0 +1,120 @@
+<?php
+
+declare(strict_types=1);
+
+namespace PhpOffice\PhpSpreadsheetTests\Style;
+
+use PhpOffice\PhpSpreadsheet\Spreadsheet;
+use PhpOffice\PhpSpreadsheet\Style\NumberFormat;
+use PHPUnit\Framework\TestCase;
+
+class NumberFormatSystemDateTimeTest extends TestCase
+{
+    private string $shortDateFormat;
+
+    private string $longDateFormat;
+
+    private string $dateTimeFormat;
+
+    private string $timeFormat;
+
+    protected function setUp(): void
+    {
+        $this->shortDateFormat = NumberFormat::getShortDateFormat();
+        $this->longDateFormat = NumberFormat::getLongDateFormat();
+        $this->dateTimeFormat = NumberFormat::getDateTimeFormat();
+        $this->timeFormat = NumberFormat::getTimeFormat();
+    }
+
+    protected function tearDown(): void
+    {
+        NumberFormat::setShortDateFormat($this->shortDateFormat);
+        NumberFormat::setLongDateFormat($this->longDateFormat);
+        NumberFormat::setDateTimeFormat($this->dateTimeFormat);
+        NumberFormat::setTimeFormat($this->timeFormat);
+    }
+
+    public function testOverrides(): void
+    {
+        $spreadsheet = new Spreadsheet();
+        $sheet = $spreadsheet->getActiveSheet();
+        $formula = '=DATEVALUE("2024-02-29")+TIMEVALUE("8:12:15 AM")';
+        $sheet->getCell('A1')->setValue($formula);
+        $sheet->getCell('A2')->setValue($formula);
+        $sheet->getStyle('A2')->getNumberFormat()
+            ->setBuiltinFormatCode(14);
+        $sheet->getCell('A3')->setValue($formula);
+        $sheet->getStyle('A3')->getNumberFormat()
+            ->setBuiltinFormatCode(15);
+        $sheet->getCell('A4')->setValue($formula);
+        $sheet->getStyle('A4')->getNumberFormat()
+            ->setBuiltinFormatCode(22);
+        $sheet->getCell('A5')->setValue($formula);
+        $sheet->getStyle('A5')->getNumberFormat()
+            ->setFormatCode('[$-F800]');
+        $sheet->getCell('A6')->setValue($formula);
+        $sheet->getStyle('A6')->getNumberFormat()
+            ->setFormatCode('[$-F400]');
+        $sheet->getCell('A7')->setValue($formula);
+        $sheet->getStyle('A7')->getNumberFormat()
+            ->setFormatCode('[$-x-sysdate]');
+        $sheet->getCell('A8')->setValue($formula);
+        $sheet->getStyle('A8')->getNumberFormat()
+            ->setFormatCode('[$-x-systime]');
+        $sheet->getCell('A9')->setValue($formula);
+        $sheet->getStyle('A9')->getNumberFormat()
+            ->setFormatCode('hello' . NumberFormat::FORMAT_SYSDATE_F800 . 'goodbye');
+        NumberFormat::setShortDateFormat('yyyy/mm/dd');
+        NumberFormat::setDateTimeFormat('yyyy/mm/dd hh:mm AM/PM');
+        NumberFormat::setLongDateFormat('dddd d mmm yyyy');
+        NumberFormat::setTimeFormat('h:mm');
+        self::assertSame('2024/02/29', $sheet->getCell('A2')->getformattedValue());
+        self::assertSame('2024/02/29 08:12 AM', $sheet->getCell('A4')->getformattedValue());
+        self::assertSame('Thursday 29 Feb 2024', $sheet->getCell('A5')->getformattedValue());
+        self::assertSame('8:12', $sheet->getCell('A6')->getformattedValue());
+        self::assertSame('Thursday 29 Feb 2024', $sheet->getCell('A7')->getformattedValue());
+        self::assertSame('8:12', $sheet->getCell('A8')->getformattedValue());
+        self::assertSame('Thursday 29 Feb 2024', $sheet->getCell('A9')->getformattedValue());
+        $spreadsheet->disconnectWorksheets();
+    }
+
+    public function testDefaults(): void
+    {
+        $spreadsheet = new Spreadsheet();
+        $sheet = $spreadsheet->getActiveSheet();
+        $formula = '=DATEVALUE("2024-02-29")+TIMEVALUE("8:12:15 AM")';
+        $sheet->getCell('A1')->setValue($formula);
+        $sheet->getCell('A2')->setValue($formula);
+        $sheet->getStyle('A2')->getNumberFormat()
+            ->setBuiltinFormatCode(14);
+        $sheet->getCell('A3')->setValue($formula);
+        $sheet->getStyle('A3')->getNumberFormat()
+            ->setBuiltinFormatCode(15);
+        $sheet->getCell('A4')->setValue($formula);
+        $sheet->getStyle('A4')->getNumberFormat()
+            ->setBuiltinFormatCode(22);
+        $sheet->getCell('A5')->setValue($formula);
+        $sheet->getStyle('A5')->getNumberFormat()
+            ->setFormatCode('[$-F800]');
+        $sheet->getCell('A6')->setValue($formula);
+        $sheet->getStyle('A6')->getNumberFormat()
+            ->setFormatCode('[$-F400]');
+        $sheet->getCell('A7')->setValue($formula);
+        $sheet->getStyle('A7')->getNumberFormat()
+            ->setFormatCode('[$-x-sysdate]');
+        $sheet->getCell('A8')->setValue($formula);
+        $sheet->getStyle('A8')->getNumberFormat()
+            ->setFormatCode('[$-x-systime]');
+        $sheet->getCell('A9')->setValue($formula);
+        $sheet->getStyle('A9')->getNumberFormat()
+            ->setFormatCode('hello' . NumberFormat::FORMAT_SYSDATE_F800 . 'goodbye');
+        self::assertSame('2/29/2024', $sheet->getCell('A2')->getformattedValue());
+        self::assertSame('2/29/2024 8:12', $sheet->getCell('A4')->getformattedValue());
+        self::assertSame('Thursday, February 29, 2024', $sheet->getCell('A5')->getformattedValue());
+        self::assertSame('8:12:15 AM', $sheet->getCell('A6')->getformattedValue());
+        self::assertSame('Thursday, February 29, 2024', $sheet->getCell('A7')->getformattedValue());
+        self::assertSame('8:12:15 AM', $sheet->getCell('A8')->getformattedValue());
+        self::assertSame('Thursday, February 29, 2024', $sheet->getCell('A9')->getformattedValue());
+        $spreadsheet->disconnectWorksheets();
+    }
+}
diff --git a/tests/data/Calculation/TextData/TEXT.php b/tests/data/Calculation/TextData/TEXT.php
index 19032d006..bf6474a28 100644
--- a/tests/data/Calculation/TextData/TEXT.php
+++ b/tests/data/Calculation/TextData/TEXT.php
@@ -81,4 +81,5 @@ return [
     'no arguments' => ['exception'],
     'one argument' => ['exception', 1.75],
     'boolean in lieu of string' => ['TRUE', true, '@'],
+    'system long date format' => ['Sunday, January 1, 2012', '1-Jan-2012', '[$-x-sysdate]'],
 ];
diff --git a/tests/data/Shared/Date/FormatCodes.php b/tests/data/Shared/Date/FormatCodes.php
index 8cd09172c..7e2c62668 100644
--- a/tests/data/Shared/Date/FormatCodes.php
+++ b/tests/data/Shared/Date/FormatCodes.php
@@ -160,4 +160,10 @@ return [
         false,
         '\D-00000',
     ],
+    [true, '[$-F800]'],
+    [true, 'hello[$-F400]goodbye'],
+    [false, '[$-F401]'],
+    [true, '[$-x-sysdate]'],
+    [true, '[$-x-systime]'],
+    [false, '[$-x-systim]'],
 ];