Question

I need a method for adding some number of months to any date in PHP. I know how to do this in MySQL but not in PHP. Here’s my attempt:

MySQL:

    SELECT DATE_ADD( '2011-12-29', INTERVAL 2
    MONTH ) // Output "2012-02-29"

    SELECT DATE_ADD( '2011-12-30', INTERVAL 2
    MONTH )  // output "2012-02-29"

    SELECT DATE_ADD( '2011-12-31', INTERVAL 2
    MONTH )  // output "2012-02-29"

PHP:

    $date = date_create('2011-12-29');
    $date->modify("+1 month");
    echo $date->format("Y-m-d");
    // Output is "2012-01-29" -- this is correct 

    $date = date_create('2011-12-30');
    $date->modify("+2 month");
    echo $date->format("Y-m-d");
    // Output is "2012-03-01" -- I need the answer like "2012-02-29" 

    $date = date_create('2011-12-31');
    $date->modify("+2 month");
    echo $date->format("Y-m-d");
    // Output is "2012-03-02" -- I need the answer like "2012-02-29" 

The MySQL output is correct. I need the same output in PHP.

Answer 1

Here’s a solution that might do the job for you:

function addMonths(DateTime $date, $months) {
    $last = clone $date;
    $last = $last->modify("last day of +$months months")->getTimestamp();

    $default = clone $date;
    $default = $default->modify("+$months months")->getTimestamp();

    return $date->setTimestamp(min($last, $default));
}

$date = new DateTime('2011-12-31');
$laterDate = addMonths($date, 2);

This will work regardless of which day of the month you start with.