PHP Date Returning Wrong Month on Subtracting One Month

PHP date returning wrong Month on subtracting one month

strtotime() uses 30 day months and there are only 28 in days in February (this year) so will not yield a valid date in February. You could use the current day d or j and subtract that which will always put you in the previous month (-29 days):

$prevmonth = date('M', strtotime('-' . date('d') . ' days'));

This will get December from January as well.

strtotime('-1 month') returning wrong date if month have 31 days

As you can see working with the end of the month can be problematic because of how PHP works with dates. Your best bet is to go back to the beginning of the month, do your date math (i.e. go backwards in time), and then go to the date you want. That way you can check to see if the current day is greater than the number of days in month. If so, use the last day of the month instead.

function getMonthsAgo(int $n): string {
    $date = new DateTime();
    $day  = $date->format('j');
    $date->modify('first day of this month')->modify('-' . $n . ' months');
    if ($day > $date->format('t')) {
        $day = $date->format('t');
    }
    $date->setDate($date->format('Y'), $date->format('m'), $day);
    return $date->format('Y-m-d');
}

// Dates Formated
$date_now = date('Y-m-d');
$date_month1 = getMonthsAgo(1);
$date_month2 = getMonthsAgo(2);
$date_month3 = getMonthsAgo(3);

//Output
echo $date_now;
echo $date_month1;
echo $date_month2;
echo $date_month3;

Output:

2020-04-30
2020-03-30
2020-02-29
2020-01-30

PHP DateTime::modify adding and subtracting months

Why it's not a bug:

The current behavior is correct. The following happens internally:

1. +1 month increases the month number (originally 1) by one. This makes the date 2010-02-31.

2. The second month (February) only has 28 days in 2010, so PHP auto-corrects this by just continuing to count days from February 1st. You then end up at March 3rd.

How to get what you want:

To get what you want is by: manually checking the next month. Then add the number of days next month has.

I hope you can yourself code this. I am just giving what-to-do.

PHP 5.3 way:

To obtain the correct behavior, you can use one of the PHP 5.3's new functionality that introduces the relative time stanza first day of. This stanza can be used in combination with next month, fifth month or +8 months to go to the first day of the specified month. Instead of +1 month from what you're doing, you can use this code to get the first day of next month like this:

<?php
$d = new DateTime( '2010-01-31' );
$d->modify( 'first day of next month' );
echo $d->format( 'F' ), "\n";
?>

This script will correctly output February. The following things happen when PHP processes this first day of next month stanza:

1. next month increases the month number (originally 1) by one. This makes the date 2010-02-31.

2. first day of sets the day number to 1, resulting in the date 2010-02-01.

PHP Date() strtotime get past month wrong

Thanks for the answers - I managed to solve it by using:

strtotime(date('Y-m')." -8 Month")

PHP DateTime::modify adding and subtracting months

Why it's not a bug:

The current behavior is correct. The following happens internally:

1. +1 month increases the month number (originally 1) by one. This makes the date 2010-02-31.

2. The second month (February) only has 28 days in 2010, so PHP auto-corrects this by just continuing to count days from February 1st. You then end up at March 3rd.

How to get what you want:

To get what you want is by: manually checking the next month. Then add the number of days next month has.

I hope you can yourself code this. I am just giving what-to-do.

PHP 5.3 way:

To obtain the correct behavior, you can use one of the PHP 5.3's new functionality that introduces the relative time stanza first day of. This stanza can be used in combination with next month, fifth month or +8 months to go to the first day of the specified month. Instead of +1 month from what you're doing, you can use this code to get the first day of next month like this:

<?php
$d = new DateTime( '2010-01-31' );
$d->modify( 'first day of next month' );
echo $d->format( 'F' ), "\n";
?>

This script will correctly output February. The following things happen when PHP processes this first day of next month stanza:

1. next month increases the month number (originally 1) by one. This makes the date 2010-02-31.

2. first day of sets the day number to 1, resulting in the date 2010-02-01.

PHP date_diff function returns wrong result

If you need the difference in months from the beginning of the first day to the end of the last day at midnight, you can also set the end date to midnight (24h !) or add a day.

<?php
$dateStart = date_create("2019-03-01");
$dateEnd = date_create("2020-01-31");

//set Time to midnight or add a day
$dateEnd->setTime(24,0,0);

$diff = date_diff($dateStart,$dateEnd);
echo $diff->format("%m months");
//11 months

try self.

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