Get first day of week in PHP?

$givenday = date("w", mktime(0, 0, 0, MM, dd, yyyy));

This gives you the day of the week of the given date itself where 0 = Sunday and 6 = Saturday. From there you can simply calculate backwards to the day you want.

How about this?

$day_of_week = date('N', strtotime($string_date));
$week_first_day = date('Y-m-d', strtotime($string_date . " - " . ($day_of_week - 1) . " days"));
$week_last_day = date('Y-m-d', strtotime($string_date . " + " . (7 - $day_of_week) . " days"));

Try this:

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)));

(from this forum thread)

$string_date = '2019-07-31';
echo $day_of_week = date('N', strtotime($string_date));
echo $week_first_day = date('Y-m-d', strtotime($string_date . " - " . ($day_of_week - 1) . " days"));
echo $week_last_day = date('Y-m-d', strtotime($string_date . " + " . (7 - $day_of_week) . " days"));

You parse the date using strptime() and use date() on the result:

date('N', strptime('%m-%d-%g', $dateString));

<?php
/* PHP 5.3.0 */

date_default_timezone_set('America/Denver'); //Set apprpriate timezone
$start_date = strtotime('2009-12-15'); //Set start date

//Today's date if $start_date is a Sunday, otherwise date of previous Sunday
$today_or_previous_sunday = mktime(0, 0, 0, date('m', $start_date), date('d', $start_date), date('Y', $start_date)) - ((date("w", $start_date) ==0) ? 0 : (86400 * date("w", $start_date)));

//prints 12-13-2009 (month-day-year)
echo date('m-d-Y', $today_or_previous_sunday);

?>

(Note: MM, dd and yyyy in the Question are not standard php date format syntax - I can't be sure what is meant, so I set the $start_date with ISO year-month-day)

I've come against this question a few times and always surprised the date functions don't make this easier or clearer. Here's my solution for PHP5 that uses the DateTime class:

/**
 * @param DateTime $date A given date
 * @param int $firstDay 0-6, Sun-Sat respectively
 * @return DateTime
 */
function getFirstDayOfWeek(DateTime $date, $firstDay = 0) {
    $offset = 7 - $firstDay;
    $ret = clone $date;
    $ret->modify(-(($date->format('w') + $offset) % 7) . 'days');
    return $ret;
}

Necessary to clone to avoid altering the original date.

Here's a one liner for the first day of last week, and the last day of last week as a DateTime object.

$firstDay = (new \DateTime())->modify(sprintf('-%d day', date('w') + 7))
                             ->setTime(0, 0, 0);
$lastDay = (new \DateTime())->modify(sprintf('-%d day', date('w') + 1))
                            ->setTime(23, 59, 59);

In order to have the simplest code and have weeks starting on monday, I used this method:

$day = (date('w')+6)%7; //transform week start from sunday to monday
$time = strtotime('-'.$day.' days');

just simply oneline answer ;)

$mondayThisWeek = new Date($date . 'this week monday');