How to Add Months to a Date in PHP Without Exceeding the Last Day of the Month?

Adding Months to Dates without Exceeding the Last Day of the Month in PHP

Modifying a date and adding months is a straightforward task in PHP. However, ensuring that the resulting date does not extend beyond the last day of the month poses a slight challenge.

To address this, we present an approach that ensures precision in date addition:

<code class="php">function add($date_str, $months)
{
    $date = new DateTime($date_str);
    
    // Capture the starting day of the month
    $start_day = $date->format('j');
    
    // Add the specified number of months
    $date->modify("+{$months} month");

    // Extract the resulting day of the month
    $end_day = $date->format('j');
    
    // Check if the resulting day differs from the original day
    if ($start_day != $end_day)
    {
        // If they are different, it means the month changed, so we adjust the date
        $date->modify('last day of last month');
    }
    
    return $date;
}</code>

This function takes two parameters: the initial date as a string and the number of months to add. It starts by creating a DateTime object and extracting the starting day of the month. The date is then modified by adding the specified number of months. After the addition, it retrieves the resulting day of the month and compares it to the original day. If the days are different, it indicates that the month has changed, so the date is corrected to the last day of the previous month.

To demonstrate the utility of this function, here are a few examples:

<code class="php">$result = add('2011-01-28', 1); // 2011-02-28
$result = add('2011-01-31', 3); // 2011-04-30
$result = add('2011-01-30', 13); // 2012-02-29
$result = add('2011-10-31', 1); // 2011-11-30
$result = add('2011-12-30', 1); // 2011-02-28</code>

By utilizing this function, you can confidently add months to dates without the concern of overruns into subsequent months.

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