date() / time() / mktime()

date($format, $timestamp);

time();

// Generates a UNIX timestamp for a specified date and time.
mktime($hour, $minute, $second, $month, $day, $year);

// Formats a date/time value in GMT and returns it as a string.
gmdate($format, $timestamp);

sample_date.php

<?php
date_default_timezone_set('Asia/Tokyo');

// Format the current date.
echo date("Y-m-d") . "\n"; // Outputs something like "2025-04-15".
echo date("F j, Y") . "\n"; // Outputs something like "April 15, 2025".

// Format the date and time together.
echo date("Y-m-d H:i:s") . "\n"; // Outputs something like "2025-04-15 10:30:45".

$week = ["Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"];
echo $week[date("w")] . "\n"; // Outputs the current day of the week.

// Get the current timestamp with time().
echo time() . "\n"; // Outputs an integer like "1744684245".

// Calculate the timestamp one hour from now.
$one_hour_later = time() + 3600;
echo date("H:i:s", $one_hour_later) . "\n"; // Outputs the time one hour from now.

// Generate a timestamp for a specific date with mktime().
$ts = mktime(0, 0, 0, 12, 31, 2025);
echo date("Y-m-d D", $ts) . "\n"; // Outputs "2025-12-31 Wed".

// Use mktime() overflow to find the last day of a month.
$last_day = mktime(0, 0, 0, 4, 0, 2025); // Day 0 of April is treated as the last day of March.
echo date("Y-m-d", $last_day) . "\n"; // Outputs "2025-03-31".

// Get the current time in GMT with gmdate().
echo gmdate("Y-m-d H:i:s") . "\n"; // Outputs the time in GMT.

// Calculate 30 days after a fictional event date.
$event_ts = mktime(0, 0, 0, 4, 1, 2025); // Fictional event date
$thirty_days_later = $event_ts + (60 * 60 * 24 * 30);
echo date("Y-m-d", $thirty_days_later) . "\n"; // Outputs the date 30 days later.

Running the code produces the following output:

php sample_date.php
2025-04-15
April 15, 2025
2025-04-15 10:30:45
Tue
1744684245
11:30:45
2025-12-31 Wed
2025-03-31
2025-04-15 01:30:45
2025-05-01

The default timezone used by date() depends on the server's php.ini configuration. To ensure a consistent timezone, call date_default_timezone_set() at the top of your script, or set date.timezone in php.ini.

<?php
// Without a timezone setting, the output depends on the server configuration.
// echo date("Y-m-d H:i:s"); // May not be in your expected timezone.

The same logic can also be written as:

<?php
date_default_timezone_set('Asia/Tokyo');
echo date("Y-m-d H:i:s"); // Outputs Japan time.

The second argument to date() must be an integer UNIX timestamp. Passing a date string directly does not work as expected. Use strtotime() to convert a string to a timestamp first.

<?php
// Passing a string produces incorrect results.
// echo date("Y-m-d", "2025-04-15"); // Does not work correctly.

The corrected version is:

<?php
// Convert the date string to a timestamp first with strtotime().
$ts = strtotime("2025-04-15");
echo date("Y-m-d", $ts); // Outputs "2025-04-15".

The arguments for mktime() are in the order: hour, minute, second, month, day, year. This is different from the year-month-day order you might expect.

<?php
// Easy to get wrong: passing year-month-day order.
// $ts = mktime(0, 0, 0, 2025, 4, 15); // Wrong: 2025 is treated as the month.

The corrected version is:

<?php
// Correct: hour, minute, second, month, day, year.
$ts = mktime(0, 0, 0, 4, 15, 2025); // April 15, 2025, 00:00:00
echo date("Y-m-d", $ts); // Outputs "2025-04-15".

Calculating elapsed days

Computing how many days have passed since a specific event.

<?php
date_default_timezone_set('Asia/Tokyo');

// Calculating elapsed days from a fictional event date.
$event_ts = mktime(0, 0, 0, 1, 6, 2025);
$today_ts = mktime(0, 0, 0, (int) date("m"), (int) date("d"), (int) date("Y"));
$diff_days = (int) (($today_ts - $event_ts) / 86400);

echo "It has been {$diff_days} days since the event.\n";

sample_elapsed.php

php sample_elapsed.php
It has been 89 days since the event.

Getting the first and last day of a month

Retrieving the first and last day of a given month.

<?php
date_default_timezone_set('Asia/Tokyo');

$year = 2025;
$month = 4;

// First day of the month.
$first_day = mktime(0, 0, 0, $month, 1, $year);
echo date("Y-m-d", $first_day) . "\n"; // Outputs "2025-04-01".

// Day 0 of next month = last day of this month.
$last_day = mktime(0, 0, 0, $month + 1, 0, $year);
echo date("Y-m-d", $last_day) . "\n"; // Outputs "2025-04-30".

sample_month_range.php

php sample_month_range.php
2025-04-01
2025-04-30

date() is one of the most commonly used date functions in PHP. You can combine format characters to build any date string you need. A convenient feature is that non-format characters are passed through as-is, so you can include literal text directly in the format string.

The UNIX timestamp returned by time() represents the number of seconds elapsed since January 1, 1970, 00:00:00 UTC. You can easily calculate past or future dates by adding or subtracting seconds from a timestamp. The timezone is configured via date.timezone in php.ini, or by calling date_default_timezone_set() in your script. For Japan, use 'Asia/Tokyo'.

For more flexible date and time manipulation, use the DateTime class. To parse a date string into a timestamp, use strtotime().