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PHP date_diff() Function

Quick summary: The PHP date_diff() function calculates the difference between two DateTime objects.

PHP date_diff() Syntax 

date_diff(DateTimeInterface $base, DateTimeInterface $target, bool $absolute = false): DateInterval
PHP

PHP date_diff() Basic examples 

$a = date_create('2026-02-01');
$b = date_create('2026-02-08');
$diff = date_diff($a, $b);
var_dump($diff->days);
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Output:
int(7)

Calculates the number of days between dates.

PHP date_diff() Real-world usage 

$start = date_create('now');
$end = date_create('+1 week');
$diff = date_diff($start, $end);
echo $diff->format('%a days');
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Output:
7 days

Measures time intervals.

PHP date_diff() Edge cases 

$a = date_create('2026-02-08');
$b = date_create('2026-02-01');
$diff = date_diff($a, $b);
var_dump($diff->invert);
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Output:
int(1)

invert indicates a negative interval.

PHP date_diff() Common mistakes

Assuming date_diff returns absolute values

Intervals can be inverted.

Incorrect
date_diff($a, $b)->days;
Correct
abs(date_diff($a, $b)->days);

Use abs() if direction does not matter.

PHP date_diff() Frequently Asked Questions

What does date_diff() do?

Calculates difference between two DateTime objects.

Return type?

DateInterval object.

Use case?

Date comparisons.

Common mistake?

Passing strings instead of objects.

Can return negative?

Yes.

Performance?

Fast.

Alternative?

Manual timestamp diff.

Supports days/months?

Yes.

Timezone aware?

Yes.

Safe?

Yes.

Best practice?

Use DateTime consistently.

Used in age calculation?

Yes.

PHP date_diff() Related PHP Functions