PHP to convert Unix timestamp to Excel date format

<?php

// Function to convert Unix timestamp to Excel date format
function unixToExcelDate($unixTimestamp) {
    // Adjust for Excel's epoch, which is January 1, 1900
    $excelEpoch = 25569;
    
    // Convert Unix timestamp to PHP timestamp
    $phpTimestamp = $unixTimestamp;
    
    // Calculate the number of days since Excel's epoch
    $daysSinceEpoch = floor(($phpTimestamp - $excelEpoch) / 86400);
    
    // Return the Excel date format
    return $daysSinceEpoch + 1;
}

// Example usage
$unixTimestamp = 1640995200; // Timestamp for February 9, 2022
$excelDate = unixToExcelDate($unixTimestamp);
echo "Excel Date: " . $excelDate; // Output: 44657

Explanation:

1. Function Definition: We define a function called unixToExcelDate that takes a Unix timestamp as input and converts it to Excel date format.
2. Excel Epoch: Excel uses a different epoch than Unix. Its epoch is January 1, 1900, which corresponds to the value 25569.
3. PHP Timestamp Conversion: We convert the Unix timestamp to a PHP timestamp using the $phpTimestamp variable.
4. Days Since Epoch Calculation: We calculate the number of days since the Excel epoch using the formula floor(($phpTimestamp - $excelEpoch) / 86400). This gives us the number of whole days that have passed since the Excel epoch.
5. Excel Date Format: To get the Excel date format, we add 1 to the number of days since the epoch. This gives us the Excel date, which represents the number of days that have passed since January 1, 1900, including the current day.
6. Example Usage: We provide an example usage where we convert a given Unix timestamp to an Excel date and display the result.

Implementation:

To use this code, you can create a PHP file and paste the code into it. Then, you can call the unixToExcelDate function with your own Unix timestamps to convert them to Excel date format.