Find week number dates with php

Question

is there a solution to find the start and the end date for a specific week number. Example:

If i enter $week = 5, i want to get 2016-03-28 - 2016-04-03. I need only for the current year.

isn't the 5° week start 2016-02-01 and end on 2016-02-07? – Federkun Apr 01 '16 at 01:00 — Federkun, Apr 01 '16 at 01:00
I think OP means month's week number – fusion3k Apr 01 '16 at 01:03 — fusion3k, Apr 01 '16 at 01:03

Brogan · Answer 1 · 2016-04-01T03:35:14.750

I think what you're looking for is strtotime and date.

<?php
$year = 2016;
$week = 1;

$a = strtotime('January 1 ' . $year);
$b = date('N', $a) - 1;
$c = $a;
$a += (7 - $b) * 86400;

if($week > 1) {
    $start = $a + (($week - 2) * 604800);
    $end = $start + ($b ? 518400 : 604800);
}
else {
    $start = $c;
    $end = $a - 86400;
}

echo date('l jS \of F Y', $start);
echo '<br />';
echo date('l jS \of F Y', $end);

Friday 1st of January 2016
Sunday 3rd of January 2016

As a function with some validation. This version will even keep the last week of the year short, like the first week, if the last week rolls into the next year. Returns false if the week does not fall within the year:

<?php
function weekdays($week, $year = false) {
    $week = floor($week);
    if($week < 0 || $week > 53)
        return false;

    if($year == false)
        $year = date('Y');

    $a = strtotime('January 1 ' . $year);
    $b = date('N', $a) - 1;
    $c = $a;
    $a += (7 - $b) * 86400;

    if($week > 1) {
        $a += (($week - 2) * 604800);
        $b = $a + ($b ? 518400 : 604800);
        return
            date('Y', $a) == $year
                ? array(
                    'first' => $a,
                    'last' =>
                        date('Y', $b) > $year
                        ? $b - (8 - date('N', $b)) * 86400
                        : $b
                ) : false;
    }
    else
        return array('first' => $c, 'last' => $a - 86400);
}

$week = weekdays(14, 2016);
echo date('l jS \of F Y', $week['first']);
echo '<br />';
echo date('l jS \of F Y', $week['last']);

Monday 28th of March 2016
Sunday 3rd of April 2016

This is not first or and day of week. This is first day of year. — fusion3k, Apr 01 '16 at 01:06
I think that “the start and the end date for a specific week” and “ i want to get 2016-03-28 - 2016-04-03” means monday/sunday. — fusion3k, Apr 01 '16 at 01:14

score 0 · Answer 2 · edited May 23 '17 at 11:45

You could use PHP relative datetime functions (http://php.net/manual/en/datetime.formats.relative.php) like:

//date_default_timezone_set('Europe/Amsterdam');
$date = new DateTime();
$date->modify('2016W5'); //First day of week 5 of 2016
$date->modify('2016W5 +6 days'); //Last day of week 5 of 2016

Or build your own function:

function week_start_date($wk_num, $yr, $first = 1, $format = 'F d, Y') 
{ 
    $wk_ts  = strtotime('+' . $wk_num . ' weeks', strtotime($yr . '0101')); 
    $mon_ts = strtotime('-' . date('w', $wk_ts) + $first . ' days', $wk_ts); 
    return date($format, $mon_ts); 
} 

$sStartDate = week_start_date($week_number, $year); 
$sEndDate   = date('F d, Y', strtotime('+6 days', strtotime($sStartDate)));

Extracted from here: Finding First day of week via php

score 0 · Accepted Answer · answered Apr 01 '16 at 01:06

You can do this with DateTime:

$year = 2016;
$week = 13;

$date = new DateTime();
$date->setISODate($year, $week);

$start = $date->format('Y-m-d');
$end = $date->modify('+6 days')->format('Y-m-d');

echo 'Week start: '. $start , "\n"; // 2016-03-28
echo 'Week end: '. $end , "\n"; // 2016-04-03

score 0 · Answer 4 · answered Apr 01 '16 at 02:13

If i enter $week = 5, i want to get 2016-03-28 - 2016-04-03.

So, I think you want monday and sunday of 5th week of march.

To obtain this, I create a simple function that require a date string (YYYY-MM-DD) and the week number. The function create a DateTime object from given string, then modify it in the first day of month, then retrieve first day of date week and add $week -1 weeks. At this point we have the first day (monday) of desired week. We clone this date to $end and we add to it 6 days.

Function returns an object with $start and $end dates as properties, obtained casting an array created by compact():

function monthWeek( $date, $week )
{
    $start = new DateTime( $date );
    $start->modify( 'first day of this month' );
    $start->modify( '-'.($start->format( 'w' )-1).' days' );
    $start->modify( '+'.($week-1).' weeks' );
    $end = clone $start;
    $end->modify( '+6 days' );
    return (object) compact( 'start', 'end' );
}

Calling above function with a casual day of march:

$week = monthWeek( '2016-03-25', 5 );

echo $week->start->format( 'l, Y-m-d' );
echo " => ";
echo $week->end->format( 'l, Y-m-d' );

we obtain this:

Monday, 2016-03-28 => Sunday, 2016-04-03

You can use the function also for retrieve year-based week, using a day of january as first arguments:

$week = monthWeek( '2016-01-25', 14 );

echo $week->start->format( 'l, Y-m-d' );
echo " => ";
echo $week->end->format( 'l, Y-m-d' );

will output:

Monday, 2016-03-28 => Sunday, 2016-04-03

phpFiddle demo

Find week number dates with php

4 Answers4