strtotime() : 'first/last day of last/this/next X" gives unexpected results when X is either week or year

[Walessio]

Description

The following code:

<?php 
$map = [
	'first day of last week'	=> '2025-08-25',	'last day of last week'	=> '2025-08-31',
	'first day of last month'	=> '2025-08-01',	'last day of last month'=> '2025-08-31',
	'first day of last year'	=> '2024-01-01',	'last day of last year'	=> '2024-12-31',
	
	'first day of this week'	=> '2025-09-01',	'last day of this week'	=> '2025-09-07',
	'first day of this month'	=> '2025-09-01',	'last day of this month'=> '2025-09-30',
	'first day of this year'	=> '2025-01-01',	'last day of this year'	=> '2025-12-31',
	
	'first day of next week'	=> '2025-09-08',	'last day of next week'	=> '2025-09-14',
	'first day of next month'	=> '2025-10-01',	'last day of next month'=> '2025-10-31',
	'first day of next year'	=> '2026-01-01',	'last day of next year'	=> '2026-12-31',
];

$time = strtotime($s = 'today');	
echo $s . "\t:\t" . date('Y-m-d H:i:s',$time) . PHP_EOL;
echo PHP_EOL;
echo "string\t\t\tresult" . PHP_EOL;
foreach ($map as $string => $date) {
	$time = strtotime($s = $string);
	echo $s . "\t" . ($d = date('Y-m-d',$time)) . "\t" . PHP_EOL; 
}
<?php

Resulted in this output:

today	:	2025-09-03 00:00:00

string			        result
first day of last week	2025-09-01	
last day of last week	2025-09-30	
first day of last month	2025-08-01	
last day of last month	2025-08-31	
first day of last year	2024-09-01	
last day of last year	2024-09-30	
first day of this week	2025-09-01	
last day of this week	2025-09-30	
first day of this month	2025-09-01	
last day of this month	2025-09-30	
first day of this year	2025-09-01	
last day of this year	2025-09-30	
first day of next week	2025-09-01	
last day of next week	2025-09-30	
first day of next month	2025-10-01	
last day of next month	2025-10-31	
first day of next year	2026-09-01	
last day of next year	2026-09-30

But I expected this output instead:

today	:	2025-09-03 00:00:00

string			        result
first day of last week	2025-08-25	
last day of last week	2025-08-31	
first day of last month	2025-08-01	
last day of last month	2025-08-31	
first day of last year	2024-01-01	
last day of last year	2024-12-31	
first day of this week	2025-09-01	
last day of this week	2025-09-07	
first day of this month	2025-09-01	
last day of this month	2025-09-30	
first day of this year	2025-01-01	
last day of this year	2025-12-31	
first day of next week	2025-09-08	
last day of next week	2025-09-14	
first day of next month	2025-10-01	
last day of next month	2025-10-31	
first day of next year	2026-01-01	
last day of next year	2026-12-31

PHP Version

PHP 8.4.10

Operating System

No response

[hormus]

Hi @Walessio welcome.
It is not possible to indicate the first day or the last day of the following week because the first day is 1 while the last day is 28/29/30 or 31.

<?php 
$map = array(
	'first day of last week'	=> '2025-08-25',	'last day of last week'	=> '2025-08-31',
	'first day of last month'	=> '2025-08-01',	'last day of last month'=> '2025-08-31',
	'first day of last year'	=> '2024-01-01',	'last day of last year'	=> '2024-12-31',
	
	'first day of this week'	=> '2025-09-01',	'last day of this week'	=> '2025-09-07',
	'first day of this month'	=> '2025-09-01',	'last day of this month'=> '2025-09-30',
	'first day of this year'	=> '2025-01-01',	'last day of this year'	=> '2025-12-31',
	
	'first day of next week'	=> '2025-09-08',	'last day of next week'	=> '2025-09-14',
	'first day of next month'	=> '2025-10-01',	'last day of next month'=> '2025-10-31',
	'first day of next year'	=> '2026-01-01',	'last day of next year'	=> '2026-12-31',
);

$s = 'today';
$time = strtotime($s);	
echo $s . "\t:\t" . date('Y-m-d H:i:s',$time) . PHP_EOL;
echo PHP_EOL;
echo "string\t\t\tresult" . PHP_EOL;
foreach ($map as $string => $date) {
    $s = $string;
    $time0 = strtotime($date . ' 00:00:00');
	$time = strtotime($s, $time0);
	echo $s . "\t" . date('Y-m-d',$time) . "\t" . date('Y-m-d', $time0) . "\t" . PHP_EOL; 
}
?>

Expected result:

today	:	2025-09-05 00:00:00

string			result
first day of last week	2025-07-01	2025-08-25	
last day of last week	2025-08-31	2025-08-31	
first day of last month	2025-07-01	2025-08-01	
last day of last month	2025-07-31	2025-08-31	
first day of last year	2023-01-01	2024-01-01	
last day of last year	2023-12-31	2024-12-31	
first day of this week	2025-09-01	2025-09-01	
last day of this week	2025-09-30	2025-09-07	
first day of this month	2025-09-01	2025-09-01	
last day of this month	2025-09-30	2025-09-30	
first day of this year	2025-01-01	2025-01-01	
last day of this year	2025-12-31	2025-12-31	
first day of next week	2025-09-01	2025-09-08	
last day of next week	2025-09-30	2025-09-14	
first day of next month	2025-11-01	2025-10-01	
last day of next month	2025-11-30	2025-10-31	
first day of next year	2027-01-01	2026-01-01	
last day of next year	2027-12-31	2026-12-31

Convert your input data:
date('Y-m-d, strtotime('last day of', strtotime('2025-08-25')))