How do I know if a particular day is a weekend?

To create a date, you have the functions mktime and gmmktime :

mktime (
  [ int $hora [, int $minuto [, int $segundo[
  , int $mes [, int $dia [, int $ano [, int $is_dst ]]]]]]]
)

Knowing this, just use what's in the question:

$dataescolhida = mktime ( 0, 0, 0, 5, 31, 2016 );

if( date( 'N', $dataescolhida ) > 5 ) { ...

Version with parameter w :

if( ( date( 'w', $dataescolhida ) % 6 ) == 0 ) { ...

The code above says if 05/31/2016 fell on a weekend.

Be careful with the order of the parameters, as PHP has no criteria, the month comes before the day.

More details at:

  

link

mktime solves this problem, @Bacco has already said the essential, here is just one more example:

function finalDeSemana($aData) {
   $dia = substr($aData, 0, 2);
   $mes = substr($aData, 3, 2);
   $ano = substr($aData, 6, 4);
   $date = date('w', mktime(0, 0, 0, $mes, $dia, $ano));

   if ($date == 6): 
      echo 'Sábado' . '<br>';
   elseif ($date == 0): 
      echo 'Domingo' . '<br>';
   else:
      echo 'Não é final de semana' . '<br>';
   endif;
}

finalDeSemana('26/07/2016');
finalDeSemana('27/07/2016');
finalDeSemana('28/07/2016');
finalDeSemana('29/07/2016');
finalDeSemana('30/07/2016');
finalDeSemana('31/07/2016');

Output:

Não é final de semana
Não é final de semana
Não é final de semana
Não é final de semana
Sábado
Domingo

I do not know of any native method that returns if it's a weekend or not, but could be implemented through a simple function:

function isWeekend($dia) {
    $mes = date('n');
    $ano = date('Y');
    $dt = DateTime::createFromFormat('j/n/Y', "$dia/$mes/$ano");
    if ((date_format($dt, 'N') === '6') || (date_format($dt, 'N') === '7')) {
        return true;
    }else{
        return false;
    }
}

Usage:

echo '<pre>';
var_dump(isWeekend(24));
echo '</pre>';

echo '<pre>';
var_dump(isWeekend(25));
echo '</pre>';

echo '<pre>';
var_dump(isWeekend(26));
echo '</pre>';

Result for code rolled today (07/26/2016):

bool(true) // para dia 24/07/2016 
bool(false) // para dia 25/07/2016 
bool(false)// para dia 26/07/2016

I hope I have helped!

You can do that too.

<?php

function checkDayFDS($day){

  $nameDay = date("D", strtotime($day));
  $fds     = "Hoje não é final de semana<hr>";  

  if ($nameDay == "Sat" || $nameDay == "Sun"){
    $fds = "Oba, hoje é final de semana<hr>";
  }

  return $fds;
}


echo checkDayFDS("2017-08-18");// Sexta 
echo checkDayFDS("2017-08-19");// Sabado
echo checkDayFDS("2017-08-20");// Domingo
echo checkDayFDS("2017-08-21");// Segunda
?>