Is Not A NAN

<?php

var_dump(NAN === NAN); // false

var_dump(is_nan(NAN)); // true

?>

NAN is a special PHP constant, which represents not-a-number: it is returned when a math function cannot calculate a value because it is out of its domain of application. For example, acos(3) returns NAN, because cos() produces values between -1 and 1.

One special situation with NAN is that it is always different from anything. So, it cannot even compare to itself.

Also, NAN is a float.

See Also

• NAN (PHP manual)

• is_nan (PHP manual)

• NAN !== NAN [Try me]

PHP Features

• nan

• php-constant

• float

Last updated: 14 July 2026