Count mondays of a month with Carbon in PHP/Laravel

helpers.php

<?php

function mondaysInMonth($month = null) {
    if ($month === null) $month = Carbon\Carbon::today()->startOfMonth();

    $nextMonth = $month->copy()->endOfMonth();

    return $month->diffInDaysFiltered(function ($date) {
        return $date->isMonday();
    }, $nextMonth);
}