PHP DateTime->diff() doesn't work correctly

Question

I met an interesting case, related to the diff() method of DateTime class.

If I try to calculate difference between two dates in months like

$datetime1 = new \DateTime('June 2019');
$datetime2 = new \DateTime('July 2019');
$interval = $datetime1->diff($datetime2);
echo $interval->format('%m');

, as result I get 0.

Why does this happen?

Print_r's:

$datetime1:

DateTime Object ( [date] => 2019-06-01 00:00:00.000000 
[timezone_type] => 3 [timezone] => Europe/Berlin )

$datetime2:

DateTime Object ( [date] => 2019-07-01 00:00:00.000000 
[timezone_type] => 3 [timezone] => Europe/Berlin )

$interval:

DateInterval Object ( [y] => 0 [m] => 0 [d] => 30 [h] => 0 [i] => 0 [s] => 0 [f] => 0 
[weekday] => 0 [weekday_behavior] => 0 [first_last_day_of] => 0 
[invert] => 0 [days] => 30 [special_type] => 0 [special_amount] => 0
 [have_weekday_relative] => 0 [have_special_relative] => 0 )

The difference is 30 days, so that would only count as some months. — jeroen, Jul 12 '19 at 12:57
And a DateInterval Object of `DateInterval Object ( [y] => 0 [m] => 1 [d] => 0 [h] => 0 [i] => 0 [s] => 0 [f] => 0 [weekday] => 0 [weekday_behavior] => 0 [first_last_day_of] => 0 [invert] => 0 [days] => 30 [special_type] => 0 [special_amount] => 0 [have_weekday_relative] => 0 [have_special_relative] => 0 )` — RiggsFolly, Jul 12 '19 at 12:58
@RiggsFolly yes, on http://sandbox.onlinephpfunctions.com/ I get 1 too. — montie, Jul 12 '19 at 13:05
`var_dump($interval);` - check what that contains. You’re likely to see `d` with value `30` in there. — misorude, Jul 12 '19 at 13:07
@VincentDecaux why it can depend of the timezone?)) What's the relation between? — montie, Jul 12 '19 at 13:08
@montie I don't know, but if somepeople have the problem, and other don't, there is somehting — Vincent Decaux, Jul 12 '19 at 13:08
If you add the 3 lines what do you get? `print_r($datetime1); print_r($datetime2); print_r($interval);` Please add result to your question as extra data — RiggsFolly, Jul 12 '19 at 13:12
Stranger! Even when I use `Europe/Berlin` as a timezone I still get `1 month` — RiggsFolly, Jul 12 '19 at 13:25
But as you can see you are getting 30 days as @jeroen was suggesting. Yea, what version of PHP are you using — RiggsFolly, Jul 12 '19 at 13:26
Even when I use `Feb 2019` and `Mar 2019` I still get `1M` using PHP7.3.3 — RiggsFolly, Jul 12 '19 at 13:29
This is already answered. Please see this https://stackoverflow.com/questions/40354442/why-does-php-datetime-diff-depend-on-time-zones — Ashok Gadri, Jul 12 '19 at 13:46
According to the comment by @AshokGadri you can use the `%a` format to get the correct number of days instead of months. — Bram Verstraten, Jul 12 '19 at 13:54
@montie please review my answer below; I have found an interest inconsistency and a possible (but imperfect) workaround. — Martin, Jul 12 '19 at 14:10

score 2 · Answer 1 · edited Jun 20 '20 at 09:12

There is big inconsistency with timezone and date handing in PHP

This appears to be a bug (in so far as the datetime format is forced to a GMT* offset, according to this comment).

*(but forcing to GMT seems inconsistent with the results established by the code below)

Setting the server timezone value to any timezone does not effect this script timezone anomaly.

Below are two cases showing what happens in different time zones:

Case 1:

The following code will output a list of results for each time zone:

$tzList = DateTimeZone::listIdentifiers(DateTimeZone::ALL);

print "Current Zone:". print_r(ini_get('date.timezone'),true)."<br>\n<BR>\n";

foreach($tzList as $tzRow) {
    $tz = new DateTimeZone($tzRow);
    //$tz = null;
    $datetime1 = new \DateTime('June 2019', $tz);
    $datetime2 = new \DateTime('July 2019', $tz);
    $interval = $datetime1->diff($datetime2, false);
    echo $interval->format('%a %m') . PHP_EOL. " :: ";

    print print_r($datetime1->getTimezone(),true)."<BR>";
}

The result of this list output shows a high (~60%) rate of 0 and the rest of 1 month .

Please see here: http://sandbox.onlinephpfunctions.com/code/b18ba13deb94d112b12630a12265363fb6c7670b

Case 2:

Setting the timezone AFTER creating the object, results in a consistent answer (albeit incorrect)

$tzList = DateTimeZone::listIdentifiers(DateTimeZone::ALL);

print "Current Zone:". print_r(ini_get('date.timezone'),true)."<br>\n<BR>\n";

foreach($tzList as $tzRow) {
    //$tz = new DateTimeZone($tzRow);
    $tz = null;
    $datetime1 = new \DateTime('June 2019', $tz);
    $datetime2 = new \DateTime('July 2019', $tz);
    $datetime1->setTimezone(new DateTimeZone($tzRow));
    $datetime2->setTimezone(new DateTimeZone($tzRow));
    $interval = $datetime1->diff($datetime2, false);
    echo $interval->format('%a %m') . PHP_EOL. " :: ";

    print print_r($datetime1->getTimezone(),true)."<BR>";
}

This output's generated here all all 30 days out; but all 0 months difference.

See code here: http://sandbox.onlinephpfunctions.com/code/7bcc62f4e36f41df71b9cb928de75a53f233d9fd

So it's your choice if you want to use sometimes correct results or universally incorrect rbut consistent results, by setting when you establish the Timezone value in the DateTime objects.

Possible Solution:

If the server timezone is correctly set to UTC "correct" timezone (that naturally returns "1" month in Case 1, then CASE 2 above works consistently across all time zones given to the DateTime objects.

Also, another working solution, in this case, is to put concrete date in front of month and year in both of arguments. Respectively: "1 June 2019" and "31 July 2019". — montie, Jul 12 '19 at 15:27

Bram Verstraten · Answer 2 · 2019-07-12T13:57:50.920

1

Can you try it by adding a timezone?

$timezones = [
    'UTC',
    'Europe/Berlin',
    'America/Belize',
    'Asia/Hong_Kong',
];

foreach ($timezones as $timezone) {
    $tz = new DateTimeZone($timezone);
    $datetime1 = new \DateTime('June 2019', $tz);
    $datetime2 = new \DateTime('July 2019', $tz);
    $interval = $datetime1->diff($datetime2);
    echo str_pad($timezone, 20, ' ').' '.$interval->format('months: %M,  day: %D,  days: %a') . PHP_EOL;
}

Result:

UTC                  months: 01,  day: 00,  days: 30
Europe/Berlin        months: 00,  day: 30,  days: 30
America/Belize       months: 01,  day: 00,  days: 30
Asia/Hong_Kong       months: 00,  day: 30,  days: 30

edited Jul 12 '19 at 13:57

answered Jul 12 '19 at 13:19

Bram Verstraten

1,414
11
24

3

UTC results in 1, where Europe/Berlin results in 0 for me – Bram Verstraten Jul 12 '19 at 13:21
Using `%a` as a format will always return the same value in days – Bram Verstraten Jul 12 '19 at 13:58

jbragagnolo · Accepted Answer · 2019-07-12T13:56:50.927

The problem is in your timezone.

There is a post explaining about it here.

See this example:

<?php

echo "----- Europe/Berlin -----\n";
date_default_timezone_set('Europe/Berlin'); 
$datetime1 = new \DateTime('June 2019');
$datetime2 = new \DateTime('July 2019');
print_r($datetime1);
print_r($datetime2);

$interval = $datetime1->diff($datetime2);
print_r($interval);

echo "%m = " . $interval->format('%m') . PHP_EOL;
echo "%a = " . $interval->format('%a') . PHP_EOL;
echo "%s = " . $interval->format('%s') . PHP_EOL;


echo "\n\n\n----- America/Sao_Paulo -----\n";
date_default_timezone_set('America/Sao_Paulo'); 
$datetime1 = new \DateTime('June 2019');
$datetime2 = new \DateTime('July 2019');
print_r($datetime1);
print_r($datetime2);

$interval = $datetime1->diff($datetime2);
print_r($interval);

echo "%m = " . $interval->format('%m') . PHP_EOL;
echo "%a = " . $interval->format('%a') . PHP_EOL;
echo "%s = " . $interval->format('%s') . PHP_EOL;

And the output:

$ php date_diff.php 
----- Europe/Berlin -----
DateTime Object
(
    [date] => 2019-06-01 00:00:00.000000
    [timezone_type] => 3
    [timezone] => Europe/Berlin
)
DateTime Object
(
    [date] => 2019-07-01 00:00:00.000000
    [timezone_type] => 3
    [timezone] => Europe/Berlin
)
DateInterval Object
(
    [y] => 0
    [m] => 0
    [d] => 30
    [h] => 0
    [i] => 0
    [s] => 0
    [f] => 0
    [weekday] => 0
    [weekday_behavior] => 0
    [first_last_day_of] => 0
    [invert] => 0
    [days] => 30
    [special_type] => 0
    [special_amount] => 0
    [have_weekday_relative] => 0
    [have_special_relative] => 0
)
%m = 0
%a = 30
%s = 0



----- America/Sao_Paulo -----
DateTime Object
(
    [date] => 2019-06-01 00:00:00.000000
    [timezone_type] => 3
    [timezone] => America/Sao_Paulo
)
DateTime Object
(
    [date] => 2019-07-01 00:00:00.000000
    [timezone_type] => 3
    [timezone] => America/Sao_Paulo
)
DateInterval Object
(
    [y] => 0
    [m] => 1
    [d] => 0
    [h] => 0
    [i] => 0
    [s] => 0
    [f] => 0
    [weekday] => 0
    [weekday_behavior] => 0
    [first_last_day_of] => 0
    [invert] => 0
    [days] => 30
    [special_type] => 0
    [special_amount] => 0
    [have_weekday_relative] => 0
    [have_special_relative] => 0
)
%m = 1
%a = 30
%s = 0

In my timezone $interval->format('%m'); is 1.

You can set timezone on your dates to calculate the difference between them.

$datetime1 = new \DateTime('June 2019', new DateTimeZone('UTC'));
$datetime2 = new \DateTime('July 2019', new DateTimeZone('UTC'));
$interval = $datetime1->diff($datetime2);
print_r($interval);
echo "%m = " . $interval->format('%m') . PHP_EOL;

$ php date_diff.php 
DateInterval Object
(
    [y] => 0
    [m] => 1
    [d] => 0
    [h] => 0
    [i] => 0
    [s] => 0
    [f] => 0
    [weekday] => 0
    [weekday_behavior] => 0
    [first_last_day_of] => 0
    [invert] => 0
    [days] => 30
    [special_type] => 0
    [special_amount] => 0
    [have_weekday_relative] => 0
    [have_special_relative] => 0
)
%m = 1

But in the real world there is no difference between month length depending on time zone... — DaszuOne, Jul 12 '19 at 13:36
I just edited the answer by adding the reference. Look: [https://stackoverflow.com/questions/40354442/why-does-php-datetime-diff-depend-on-time-zones] — jbragagnolo, Jul 12 '19 at 14:02

PHP DateTime->diff() doesn't work correctly

3 Answers3

There is big inconsistency with timezone and date handing in PHP

Case 1:

Case 2:

Possible Solution: