validation - php date - check if it's under 1 month -

i checking if date less 1 months now. have working this

$entereddate < date("ymd", mktime(0, 0, 0, date("m")+1, date("d"), date("y"))) 

but instead of big line, want put date("ymd", mktime(0, 0, 0, date("m")+1, date("d"), date("y"))) inside function , call compare $entereddate < ....

is there other easy way check. checked checkdate couldn't use here.

how using function? or should complete check inside function , use in places..please give me hint.

function lessthanonemonthfromnow($unixtime) {     return ($unixtime < strototime('+1 month'));  }