DateTimeInterface
PHP Manual

DateTimeInterface::diff

DateTimeImmutable::diff

DateTime::diff

date_diff

Returns the difference between two DateTime objects

Description

Object-oriented style

public DateInterval DateTimeInterface::diff(DateTimeInterface $targetObject, bool $absolute = false)
public DateInterval DateTimeImmutable::diff(DateTimeInterface $targetObject, bool $absolute = false)
public DateInterval DateTime::diff(DateTimeInterface $targetObject, bool $absolute = false)

Procedural style

DateInterval date_diff(DateTimeInterface $baseObject, DateTimeInterface $targetObject, bool $absolute = false)

Returns the difference between two DateTimeInterface objects.

Parameters

datetime

The date to compare to.

absolute

Should the interval be forced to be positive?

Return Values

The DateInterval object represents the difference between the two dates.

The absolute parameter only affects the invert property of a DateInterval object.

The return value more specifically represents the clock-time interval to apply to the original object ($this or $originObject) to arrive at the $targetObject. This process is not always reversible.

The method is aware of DST changeovers, and hence can return an interval of 24 hours and 30 minutes, as per one of the examples. If you want to calculate with absolute time, you need to convert both the $this/$baseObject, and $targetObject to UTC first.

Examples

Example #1 DateTimeImmutable::diff example

Object-oriented style

<?php
$origin = new DateTimeImmutable('2009-10-11');
$target = new DateTimeImmutable('2009-10-13');
$interval = $origin->diff($target);
echo $interval->format('%R%a days');
?>

Procedural style

<?php
$origin = date_create('2009-10-11');
$target = date_create('2009-10-13');
$interval = date_diff($origin, $target);
echo $interval->format('%R%a days');
?>

The above examples will output:

+2 days

Example #2 DateTimeInterface::diff during DST changeover

<?php
$originalTime = new DateTimeImmutable("2021-10-30 09:00:00 Europe/London");
$targetTime = new DateTimeImmutable("2021-10-31 08:30:00 Europe/London");
$interval = $originalTime->diff($targetTime);
echo $interval->format("%H:%I:%S (Full days: %a)"), "\n";
?>

The above example will output:

24:30:00 (Full days: 0)

Example #3 DateTimeInterface::diff range

The value that the method returns is the exact amount of time to get from $this to $targetObject. Comparing January 1st to December 31st returns therefore 364, and not 365, days (for non-leap years). 

<?php
$originalTime = new DateTimeImmutable("2023-01-01 UTC");
$targetTime = new DateTimeImmutable("2023-12-31 UTC");
$interval = $originalTime->diff($targetTime);
echo "Full days: ", $interval->format("%a"), "\n";
?>

The above example will output:

Full days: 364

Example #4 DateTime object comparison

Note:

DateTimeImmutable and DateTime objects can be compared using comparison operators. 

<?php
$date1 = new DateTime("now");
$date2 = new DateTime("tomorrow");

var_dump($date1 == $date2);
var_dump($date1 < $date2);
var_dump($date1 > $date2);
?>

The above example will output:

bool(false)
bool(true)
bool(false)

See Also

  • DateInterval::format
  • DateTime::add
  • DateTime::sub