diff --git a/phpstan-baseline.neon b/phpstan-baseline.neon
index 316663bb11..085cf964cd 100644
--- a/phpstan-baseline.neon
+++ b/phpstan-baseline.neon
@@ -990,11 +990,6 @@ parameters:
 			count: 6
 			path: src/PhpSpreadsheet/Cell/Cell.php
 
-		-
-			message: "#^Unreachable statement \\- code above always terminates\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Cell/Cell.php
-
 		-
 			message: "#^Call to an undefined method object\\:\\:getHashCode\\(\\)\\.$#"
 			count: 1
diff --git a/src/PhpSpreadsheet/Cell/Cell.php b/src/PhpSpreadsheet/Cell/Cell.php
index 56b5f5f8ca..e8594506f6 100644
--- a/src/PhpSpreadsheet/Cell/Cell.php
+++ b/src/PhpSpreadsheet/Cell/Cell.php
@@ -176,16 +176,21 @@ public function getValue()
 
     /**
      * Get cell value with formatting.
-     *
-     * @return string
      */
-    public function getFormattedValue()
+    public function getFormattedValue(): string
     {
-        return (string) NumberFormat::toFormattedString(
+        $currentCalendar = SharedDate::getExcelCalendar();
+        SharedDate::setExcelCalendar($this->getWorksheet()->getParent()->getExcelCalendar());
+
+        $formattedValue = (string) NumberFormat::toFormattedString(
             $this->getCalculatedValue(),
             $this->getStyle()
                 ->getNumberFormat()->getFormatCode()
         );
+
+        SharedDate::setExcelCalendar($currentCalendar);
+
+        return $formattedValue;
     }
 
     /**
@@ -342,8 +347,6 @@ public function setValueExplicit($value, $dataType, bool $isArrayFormula = false
                 break;
             default:
                 throw new Exception('Invalid datatype: ' . $dataType);
-
-                break;
         }
 
         // set the datatype
@@ -402,6 +405,9 @@ private function processArrayResult(
     public function getCalculatedValue(bool $asArray = false, bool $resetLog = true)
     {
         if ($this->dataType === DataType::TYPE_FORMULA) {
+            $currentCalendar = SharedDate::getExcelCalendar();
+            SharedDate::setExcelCalendar($this->getWorksheet()->getParent()->getExcelCalendar());
+
             try {
                 $coordinate = $this->getCoordinate();
                 $worksheet = $this->getWorksheet();
@@ -430,6 +436,7 @@ public function getCalculatedValue(bool $asArray = false, bool $resetLog = true)
                 $this->getWorksheet()->setSelectedCells($selected);
                 $this->getWorksheet()->getParent()->setActiveSheetIndex($index);
             } catch (Exception $ex) {
+                SharedDate::setExcelCalendar($currentCalendar);
                 if (($ex->getMessage() === 'Unable to access External Workbook') && ($this->calculatedValue !== null)) {
                     return $this->calculatedValue; // Fallback for calculations referencing external files.
                 } elseif (preg_match('/[Uu]ndefined (name|offset: 2|array key 2)/', $ex->getMessage()) === 1) {
@@ -441,6 +448,7 @@ public function getCalculatedValue(bool $asArray = false, bool $resetLog = true)
                 );
             }
 
+            SharedDate::setExcelCalendar($currentCalendar);
             if ($result === '#Not Yet Implemented') {
                 return $this->calculatedValue; // Fallback if calculation engine does not support the formula.
             }
diff --git a/src/PhpSpreadsheet/Reader/Xls.php b/src/PhpSpreadsheet/Reader/Xls.php
index 9aee18ee18..98de1c029d 100644
--- a/src/PhpSpreadsheet/Reader/Xls.php
+++ b/src/PhpSpreadsheet/Reader/Xls.php
@@ -2026,9 +2026,9 @@ private function readDateMode(): void
         $this->pos += 4 + $length;
 
         // offset: 0; size: 2; 0 = base 1900, 1 = base 1904
-        Date::setExcelCalendar(Date::CALENDAR_WINDOWS_1900);
+        $this->spreadsheet->setExcelCalendar(Date::CALENDAR_WINDOWS_1900);
         if (ord($recordData[0]) == 1) {
-            Date::setExcelCalendar(Date::CALENDAR_MAC_1904);
+            $this->spreadsheet->setExcelCalendar(Date::CALENDAR_MAC_1904);
         }
     }
 
diff --git a/src/PhpSpreadsheet/Reader/Xlsx.php b/src/PhpSpreadsheet/Reader/Xlsx.php
index f793a66ae6..8f88f29412 100644
--- a/src/PhpSpreadsheet/Reader/Xlsx.php
+++ b/src/PhpSpreadsheet/Reader/Xlsx.php
@@ -681,11 +681,11 @@ protected function loadSpreadsheetFromFile(string $filename): Spreadsheet
 
                     // Set base date
                     if ($xmlWorkbookNS->workbookPr) {
-                        Date::setExcelCalendar(Date::CALENDAR_WINDOWS_1900);
+                        $excel->setExcelCalendar(Date::CALENDAR_WINDOWS_1900);
                         $attrs1904 = self::getAttributes($xmlWorkbookNS->workbookPr);
                         if (isset($attrs1904['date1904'])) {
                             if (self::boolean((string) $attrs1904['date1904'])) {
-                                Date::setExcelCalendar(Date::CALENDAR_MAC_1904);
+                                $excel->setExcelCalendar(Date::CALENDAR_MAC_1904);
                             }
                         }
                     }
diff --git a/src/PhpSpreadsheet/Shared/Date.php b/src/PhpSpreadsheet/Shared/Date.php
index 8cac2c63e8..547e875ca7 100644
--- a/src/PhpSpreadsheet/Shared/Date.php
+++ b/src/PhpSpreadsheet/Shared/Date.php
@@ -67,7 +67,7 @@ class Date
     protected static $defaultTimeZone;
 
     /**
-     * Set the Excel calendar (Windows 1900 or Mac 1904).
+     * Set the Excel Date Calendar (Windows 1900 or Mac 1904) used for calculations and formatting.
      *
      * @param int $baseYear Excel base date (1900 or 1904)
      *
@@ -85,7 +85,8 @@ public static function setExcelCalendar($baseYear)
     }
 
     /**
-     * Return the Excel calendar (Windows 1900 or Mac 1904).
+     * Return the Excel Date Calendar (Windows 1900 or Mac 1904)
+     *     to be used for current calculations and formatting.
      *
      * @return int Excel base date (1900 or 1904)
      */
diff --git a/src/PhpSpreadsheet/Spreadsheet.php b/src/PhpSpreadsheet/Spreadsheet.php
index 4bb9398712..ab2196e8b1 100644
--- a/src/PhpSpreadsheet/Spreadsheet.php
+++ b/src/PhpSpreadsheet/Spreadsheet.php
@@ -4,6 +4,7 @@
 
 use PhpOffice\PhpSpreadsheet\Calculation\Calculation;
 use PhpOffice\PhpSpreadsheet\Reader\Xlsx as XlsxReader;
+use PhpOffice\PhpSpreadsheet\Shared\Date;
 use PhpOffice\PhpSpreadsheet\Shared\File;
 use PhpOffice\PhpSpreadsheet\Shared\StringHelper;
 use PhpOffice\PhpSpreadsheet\Style\Style;
@@ -13,7 +14,7 @@
 
 class Spreadsheet
 {
-    // Allowable values for workbook window visilbity
+    // Allowable values for workbook window visibility
     const VISIBILITY_VISIBLE = 'visible';
     const VISIBILITY_HIDDEN = 'hidden';
     const VISIBILITY_VERY_HIDDEN = 'veryHidden';
@@ -55,6 +56,14 @@ class Spreadsheet
      */
     private $workSheetCollection = [];
 
+    /**
+     * Base calendar year to use for calculations
+     * Value is either CALENDAR_WINDOWS_1900 (1900) or CALENDAR_MAC_1904 (1904).
+     *
+     * @var int
+     */
+    protected $excelCalendar = Date::CALENDAR_WINDOWS_1900;
+
     /**
      * Calculation Engine.
      *
@@ -202,6 +211,34 @@ class Spreadsheet
      */
     private $tabRatio = 600;
 
+    /**
+     * Set the Excel Calendar (Windows 1900 or Mac 1904).
+     *
+     * @param int $baseYear Excel base date (1900 or 1904)
+     *
+     * @return bool Success or failure
+     */
+    public function setExcelCalendar(int $baseYear): bool
+    {
+        if (($baseYear == Date::CALENDAR_WINDOWS_1900) || ($baseYear == Date::CALENDAR_MAC_1904)) {
+            $this->excelCalendar = $baseYear;
+
+            return true;
+        }
+
+        return false;
+    }
+
+    /**
+     * Return the Excel Calendar (Windows 1900 or Mac 1904).
+     *
+     * @return int Excel base date (1900 or 1904)
+     */
+    public function getExcelCalendar(): int
+    {
+        return $this->excelCalendar;
+    }
+
     /**
      * The workbook has macros ?
      *
diff --git a/src/PhpSpreadsheet/Writer/Xls/Workbook.php b/src/PhpSpreadsheet/Writer/Xls/Workbook.php
index ccffa181b6..876f2bded0 100644
--- a/src/PhpSpreadsheet/Writer/Xls/Workbook.php
+++ b/src/PhpSpreadsheet/Writer/Xls/Workbook.php
@@ -960,9 +960,9 @@ private function writeDateMode(): void
         $record = 0x0022; // Record identifier
         $length = 0x0002; // Bytes to follow
 
-        $f1904 = (Date::getExcelCalendar() === Date::CALENDAR_MAC_1904)
-            ? 1
-            : 0; // Flag for 1904 date system
+        $f1904 = ($this->spreadsheet->getExcelCalendar() === Date::CALENDAR_MAC_1904)
+            ? 1  // Flag for 1904 date system
+            : 0; // Flag for 1900 date system
 
         $header = pack('vv', $record, $length);
         $data = pack('v', $f1904);
diff --git a/src/PhpSpreadsheet/Writer/Xlsx/Workbook.php b/src/PhpSpreadsheet/Writer/Xlsx/Workbook.php
index f9d7197d7a..176039d660 100644
--- a/src/PhpSpreadsheet/Writer/Xlsx/Workbook.php
+++ b/src/PhpSpreadsheet/Writer/Xlsx/Workbook.php
@@ -39,7 +39,7 @@ public function writeWorkbook(Spreadsheet $spreadsheet, $recalcRequired = false)
         $this->writeFileVersion($objWriter);
 
         // workbookPr
-        $this->writeWorkbookPr($objWriter);
+        $this->writeWorkbookPr($objWriter, $spreadsheet);
 
         // workbookProtection
         $this->writeWorkbookProtection($objWriter, $spreadsheet);
@@ -80,11 +80,11 @@ private function writeFileVersion(XMLWriter $objWriter): void
     /**
      * Write WorkbookPr.
      */
-    private function writeWorkbookPr(XMLWriter $objWriter): void
+    private function writeWorkbookPr(XMLWriter $objWriter, Spreadsheet $spreadsheet): void
     {
         $objWriter->startElement('workbookPr');
 
-        if (Date::getExcelCalendar() === Date::CALENDAR_MAC_1904) {
+        if ($spreadsheet->getExcelCalendar() === Date::CALENDAR_MAC_1904) {
             $objWriter->writeAttribute('date1904', '1');
         }
 
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/AllSetupTeardown.php b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/AllSetupTeardown.php
index 9fb5dfa58b..0cb3b62bd2 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/AllSetupTeardown.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/AllSetupTeardown.php
@@ -55,9 +55,13 @@ protected function tearDown(): void
         }
     }
 
-    protected static function setMac1904(): void
+    protected static function setMac1904(?Worksheet $worksheet = null): void
     {
-        Date::setExcelCalendar(Date::CALENDAR_MAC_1904);
+        if ($worksheet === null) {
+            Date::setExcelCalendar(Date::CALENDAR_MAC_1904);
+        } else {
+            $worksheet->getParent()->setExcelCalendar(Date::CALENDAR_MAC_1904);
+        }
     }
 
     protected static function setUnixReturn(): void
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/IsoWeekNumTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/IsoWeekNumTest.php
index a6615ff623..86b1389ba4 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/IsoWeekNumTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/IsoWeekNumTest.php
@@ -35,8 +35,8 @@ public function providerISOWEEKNUM(): array
     public function testISOWEEKNUM1904($expectedResult, $dateValue): void
     {
         $this->mightHaveException($expectedResult);
-        self::setMac1904();
         $sheet = $this->getSheet();
+        self::setMac1904($sheet);
         $sheet->getCell('A1')->setValue("=ISOWEEKNUM($dateValue)");
         $sheet->getCell('B1')->setValue('1954-11-23');
         self::assertSame($expectedResult, $sheet->getCell('A1')->getCalculatedValue());
diff --git a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/WeekNumTest.php b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/WeekNumTest.php
index 65b00516e0..c1c2fe774e 100644
--- a/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/WeekNumTest.php
+++ b/tests/PhpSpreadsheetTests/Calculation/Functions/DateTime/WeekNumTest.php
@@ -33,8 +33,8 @@ public function providerWEEKNUM(): array
     public function testWEEKNUM1904($expectedResult, string $formula): void
     {
         $this->mightHaveException($expectedResult);
-        self::setMac1904();
         $sheet = $this->getSheet();
+        self::setMac1904($sheet);
         $sheet->getCell('B1')->setValue('1954-11-23');
         $sheet->getCell('A1')->setValue("=WEEKNUM($formula)");
         self::assertSame($expectedResult, $sheet->getCell('A1')->getCalculatedValue());
diff --git a/tests/PhpSpreadsheetTests/Reader/Xls/DateReaderTest.php b/tests/PhpSpreadsheetTests/Reader/Xls/DateReaderTest.php
new file mode 100644
index 0000000000..5ba83166bc
--- /dev/null
+++ b/tests/PhpSpreadsheetTests/Reader/Xls/DateReaderTest.php
@@ -0,0 +1,117 @@
+<?php
+
+namespace PhpOffice\PhpSpreadsheetTests\Reader\Xls;
+
+use PhpOffice\PhpSpreadsheet\Reader\Xls;
+use PhpOffice\PhpSpreadsheet\Shared\Date;
+use PHPUnit\Framework\TestCase;
+
+class DateReaderTest extends TestCase
+{
+    protected function tearDown(): void
+    {
+        Date::setExcelCalendar(Date::CALENDAR_WINDOWS_1900);
+    }
+
+    public function testReadExcel1900Spreadsheet(): void
+    {
+        $filename = 'tests/data/Reader/XLS/1900_Calendar.xls';
+        $reader = new Xls();
+        $spreadsheet = $reader->load($filename);
+
+        self::assertSame(Date::CALENDAR_WINDOWS_1900, $spreadsheet->getExcelCalendar());
+
+        $worksheet = $spreadsheet->getActiveSheet();
+        self::assertSame(44562, $worksheet->getCell('A1')->getValue());
+        self::assertSame('2022-01-01', $worksheet->getCell('A1')->getFormattedValue());
+        self::assertSame(44926, $worksheet->getCell('A2')->getValue());
+        self::assertSame('2022-12-31', $worksheet->getCell('A2')->getFormattedValue());
+    }
+
+    public function testReadExcel1904Spreadsheet(): void
+    {
+        $filename = 'tests/data/Reader/XLS/1904_Calendar.xls';
+        $reader = new Xls();
+        $spreadsheet = $reader->load($filename);
+
+        self::assertSame(Date::CALENDAR_MAC_1904, $spreadsheet->getExcelCalendar());
+
+        $worksheet = $spreadsheet->getActiveSheet();
+        self::assertSame(43100, $worksheet->getCell('A1')->getValue());
+        self::assertSame('2022-01-01', $worksheet->getCell('A1')->getFormattedValue());
+        self::assertSame(43464, $worksheet->getCell('A2')->getValue());
+        self::assertSame('2022-12-31', $worksheet->getCell('A2')->getFormattedValue());
+    }
+
+    public function testNewDateInLoadedExcel1900Spreadsheet(): void
+    {
+        $filename = 'tests/data/Reader/XLS/1900_Calendar.xls';
+        $reader = new Xls();
+        $spreadsheet = $reader->load($filename);
+
+        $worksheet = $spreadsheet->getActiveSheet();
+        $worksheet->getCell('A4')->setValue('=DATE(2023,1,1)');
+        self::assertEquals(44927, $worksheet->getCell('A4')->getCalculatedValue());
+    }
+
+    public function testNewDateInLoadedExcel1904Spreadsheet(): void
+    {
+        $filename = 'tests/data/Reader/XLS/1904_Calendar.xls';
+        $reader = new Xls();
+        $spreadsheet = $reader->load($filename);
+
+        $worksheet = $spreadsheet->getActiveSheet();
+        $worksheet->getCell('A4')->setValue('=DATE(2023,1,1)');
+        self::assertEquals(43465, $worksheet->getCell('A4')->getCalculatedValue());
+    }
+
+    public function testSwitchCalendars(): void
+    {
+        $filename1900 = 'tests/data/Reader/XLS/1900_Calendar.xls';
+        $reader1900 = new Xls();
+        $spreadsheet1900 = $reader1900->load($filename1900);
+        $worksheet1900 = $spreadsheet1900->getActiveSheet();
+
+        $filename1904 = 'tests/data/Reader/XLS/1904_Calendar.xls';
+        $reader1904 = new Xls();
+        $spreadsheet1904 = $reader1904->load($filename1904);
+        $worksheet1904 = $spreadsheet1904->getActiveSheet();
+
+        self::assertSame(44562, $worksheet1900->getCell('A1')->getValue());
+        self::assertSame('2022-01-01', $worksheet1900->getCell('A1')->getFormattedValue());
+        self::assertSame(44926, $worksheet1900->getCell('A2')->getValue());
+        self::assertSame('2022-12-31', $worksheet1900->getCell('A2')->getFormattedValue());
+        self::assertSame(44561, $worksheet1900->getCell('B1')->getCalculatedValue());
+        self::assertSame('2021-12-31', $worksheet1900->getCell('B1')->getFormattedValue());
+        self::assertSame(44927, $worksheet1900->getCell('B2')->getCalculatedValue());
+        self::assertSame('2023-01-01', $worksheet1900->getCell('B2')->getFormattedValue());
+
+        self::assertSame(43100, $worksheet1904->getCell('A1')->getValue());
+        self::assertSame('2022-01-01', $worksheet1904->getCell('A1')->getFormattedValue());
+        self::assertSame(43464, $worksheet1904->getCell('A2')->getValue());
+        self::assertSame('2022-12-31', $worksheet1904->getCell('A2')->getFormattedValue());
+        self::assertSame(43099, $worksheet1904->getCell('B1')->getCalculatedValue());
+        self::assertSame('2021-12-31', $worksheet1904->getCell('B1')->getFormattedValue());
+        self::assertSame(43465, $worksheet1904->getCell('B2')->getCalculatedValue());
+        self::assertSame('2023-01-01', $worksheet1904->getCell('B2')->getFormattedValue());
+
+        // Check that accessing date values from one spreadsheet doesn't break accessing correct values from another
+        self::assertSame(44561, $worksheet1900->getCell('B1')->getCalculatedValue());
+        self::assertSame('2021-12-31', $worksheet1900->getCell('B1')->getFormattedValue());
+        self::assertSame(44927, $worksheet1900->getCell('B2')->getCalculatedValue());
+        self::assertSame('2023-01-01', $worksheet1900->getCell('B2')->getFormattedValue());
+        self::assertSame(44562, $worksheet1900->getCell('A1')->getValue());
+        self::assertSame('2022-01-01', $worksheet1900->getCell('A1')->getFormattedValue());
+        self::assertSame(44926, $worksheet1900->getCell('A2')->getValue());
+        self::assertSame('2022-12-31', $worksheet1900->getCell('A2')->getFormattedValue());
+
+        self::assertSame(43099, $worksheet1904->getCell('B1')->getCalculatedValue());
+        self::assertSame('2021-12-31', $worksheet1904->getCell('B1')->getFormattedValue());
+        self::assertSame(43465, $worksheet1904->getCell('B2')->getCalculatedValue());
+        self::assertSame('2023-01-01', $worksheet1904->getCell('B2')->getFormattedValue());
+        self::assertSame(43100, $worksheet1904->getCell('A1')->getValue());
+        self::assertSame('2022-01-01', $worksheet1904->getCell('A1')->getFormattedValue());
+        self::assertSame(43464, $worksheet1904->getCell('A2')->getValue());
+        self::assertSame('2022-12-31', $worksheet1904->getCell('A2')->getFormattedValue());
+    }
+}
diff --git a/tests/PhpSpreadsheetTests/Reader/Xlsx/DateReaderTest.php b/tests/PhpSpreadsheetTests/Reader/Xlsx/DateReaderTest.php
new file mode 100644
index 0000000000..042683f9c3
--- /dev/null
+++ b/tests/PhpSpreadsheetTests/Reader/Xlsx/DateReaderTest.php
@@ -0,0 +1,125 @@
+<?php
+
+namespace PhpOffice\PhpSpreadsheetTests\Reader\Xlsx;
+
+use PhpOffice\PhpSpreadsheet\Reader\Xlsx;
+use PhpOffice\PhpSpreadsheet\Shared\Date;
+use PHPUnit\Framework\TestCase;
+
+class DateReaderTest extends TestCase
+{
+    protected function tearDown(): void
+    {
+        Date::setExcelCalendar(Date::CALENDAR_WINDOWS_1900);
+    }
+
+    public function testReadExcel1900Spreadsheet(): void
+    {
+        $filename = 'tests/data/Reader/XLSX/1900_Calendar.xlsx';
+        $reader = new Xlsx();
+        $spreadsheet = $reader->load($filename);
+
+        self::assertSame(Date::CALENDAR_WINDOWS_1900, $spreadsheet->getExcelCalendar());
+
+        $worksheet = $spreadsheet->getActiveSheet();
+        self::assertSame(44562, $worksheet->getCell('A1')->getValue());
+        self::assertSame('2022-01-01', $worksheet->getCell('A1')->getFormattedValue());
+        self::assertSame(44926, $worksheet->getCell('A2')->getValue());
+        self::assertSame('2022-12-31', $worksheet->getCell('A2')->getFormattedValue());
+        self::assertSame(44561, $worksheet->getCell('B1')->getCalculatedValue());
+        self::assertSame('2021-12-31', $worksheet->getCell('B1')->getFormattedValue());
+        self::assertSame(44927, $worksheet->getCell('B2')->getCalculatedValue());
+        self::assertSame('2023-01-01', $worksheet->getCell('B2')->getFormattedValue());
+    }
+
+    public function testReadExcel1904Spreadsheet(): void
+    {
+        $filename = 'tests/data/Reader/XLSX/1904_Calendar.xlsx';
+        $reader = new Xlsx();
+        $spreadsheet = $reader->load($filename);
+
+        self::assertSame(Date::CALENDAR_MAC_1904, $spreadsheet->getExcelCalendar());
+
+        $worksheet = $spreadsheet->getActiveSheet();
+        self::assertSame(43100, $worksheet->getCell('A1')->getValue());
+        self::assertSame('2022-01-01', $worksheet->getCell('A1')->getFormattedValue());
+        self::assertSame(43464, $worksheet->getCell('A2')->getValue());
+        self::assertSame('2022-12-31', $worksheet->getCell('A2')->getFormattedValue());
+        self::assertSame(43099, $worksheet->getCell('B1')->getCalculatedValue());
+        self::assertSame('2021-12-31', $worksheet->getCell('B1')->getFormattedValue());
+        self::assertSame(43465, $worksheet->getCell('B2')->getCalculatedValue());
+        self::assertSame('2023-01-01', $worksheet->getCell('B2')->getFormattedValue());
+    }
+
+    public function testNewDateInLoadedExcel1900Spreadsheet(): void
+    {
+        $filename = 'tests/data/Reader/XLSX/1900_Calendar.xlsx';
+        $reader = new Xlsx();
+        $spreadsheet = $reader->load($filename);
+
+        $worksheet = $spreadsheet->getActiveSheet();
+        $worksheet->getCell('A4')->setValue('=DATE(2023,1,1)');
+        self::assertEquals(44927, $worksheet->getCell('A4')->getCalculatedValue());
+    }
+
+    public function testNewDateInLoadedExcel1904Spreadsheet(): void
+    {
+        $filename = 'tests/data/Reader/XLSX/1904_Calendar.xlsx';
+        $reader = new Xlsx();
+        $spreadsheet = $reader->load($filename);
+
+        $worksheet = $spreadsheet->getActiveSheet();
+        $worksheet->getCell('A4')->setValue('=DATE(2023,1,1)');
+        self::assertEquals(43465, $worksheet->getCell('A4')->getCalculatedValue());
+    }
+
+    public function testSwitchCalendars(): void
+    {
+        $filename1900 = 'tests/data/Reader/XLSX/1900_Calendar.xlsx';
+        $reader1900 = new Xlsx();
+        $spreadsheet1900 = $reader1900->load($filename1900);
+        $worksheet1900 = $spreadsheet1900->getActiveSheet();
+
+        $filename1904 = 'tests/data/Reader/XLSX/1904_Calendar.xlsx';
+        $reader1904 = new Xlsx();
+        $spreadsheet1904 = $reader1904->load($filename1904);
+        $worksheet1904 = $spreadsheet1904->getActiveSheet();
+
+        self::assertSame(44562, $worksheet1900->getCell('A1')->getValue());
+        self::assertSame('2022-01-01', $worksheet1900->getCell('A1')->getFormattedValue());
+        self::assertSame(44926, $worksheet1900->getCell('A2')->getValue());
+        self::assertSame('2022-12-31', $worksheet1900->getCell('A2')->getFormattedValue());
+        self::assertSame(44561, $worksheet1900->getCell('B1')->getCalculatedValue());
+        self::assertSame('2021-12-31', $worksheet1900->getCell('B1')->getFormattedValue());
+        self::assertSame(44927, $worksheet1900->getCell('B2')->getCalculatedValue());
+        self::assertSame('2023-01-01', $worksheet1900->getCell('B2')->getFormattedValue());
+
+        self::assertSame(43100, $worksheet1904->getCell('A1')->getValue());
+        self::assertSame('2022-01-01', $worksheet1904->getCell('A1')->getFormattedValue());
+        self::assertSame(43464, $worksheet1904->getCell('A2')->getValue());
+        self::assertSame('2022-12-31', $worksheet1904->getCell('A2')->getFormattedValue());
+        self::assertSame(43099, $worksheet1904->getCell('B1')->getCalculatedValue());
+        self::assertSame('2021-12-31', $worksheet1904->getCell('B1')->getFormattedValue());
+        self::assertSame(43465, $worksheet1904->getCell('B2')->getCalculatedValue());
+        self::assertSame('2023-01-01', $worksheet1904->getCell('B2')->getFormattedValue());
+
+        // Check that accessing date values from one spreadsheet doesn't break accessing correct values from another
+        self::assertSame(44561, $worksheet1900->getCell('B1')->getCalculatedValue());
+        self::assertSame('2021-12-31', $worksheet1900->getCell('B1')->getFormattedValue());
+        self::assertSame(44927, $worksheet1900->getCell('B2')->getCalculatedValue());
+        self::assertSame('2023-01-01', $worksheet1900->getCell('B2')->getFormattedValue());
+        self::assertSame(44562, $worksheet1900->getCell('A1')->getValue());
+        self::assertSame('2022-01-01', $worksheet1900->getCell('A1')->getFormattedValue());
+        self::assertSame(44926, $worksheet1900->getCell('A2')->getValue());
+        self::assertSame('2022-12-31', $worksheet1900->getCell('A2')->getFormattedValue());
+
+        self::assertSame(43099, $worksheet1904->getCell('B1')->getCalculatedValue());
+        self::assertSame('2021-12-31', $worksheet1904->getCell('B1')->getFormattedValue());
+        self::assertSame(43465, $worksheet1904->getCell('B2')->getCalculatedValue());
+        self::assertSame('2023-01-01', $worksheet1904->getCell('B2')->getFormattedValue());
+        self::assertSame(43100, $worksheet1904->getCell('A1')->getValue());
+        self::assertSame('2022-01-01', $worksheet1904->getCell('A1')->getFormattedValue());
+        self::assertSame(43464, $worksheet1904->getCell('A2')->getValue());
+        self::assertSame('2022-12-31', $worksheet1904->getCell('A2')->getFormattedValue());
+    }
+}
diff --git a/tests/data/Reader/XLS/1900_Calendar.xls b/tests/data/Reader/XLS/1900_Calendar.xls
new file mode 100644
index 0000000000..714670a7dc
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diff --git a/tests/data/Reader/XLS/1904_Calendar.xls b/tests/data/Reader/XLS/1904_Calendar.xls
new file mode 100644
index 0000000000..cde7fc1931
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diff --git a/tests/data/Reader/XLSX/1900_Calendar.xlsx b/tests/data/Reader/XLSX/1900_Calendar.xlsx
new file mode 100644
index 0000000000..dfd78efc7c
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diff --git a/tests/data/Reader/XLSX/1904_Calendar.xlsx b/tests/data/Reader/XLSX/1904_Calendar.xlsx
new file mode 100644
index 0000000000..f3a8a12d8e
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