Javascript checkbox if condition

I wanted to trigger an if condition based on a checked or unchecked checkbox, by clicking a button. The code segments of interest are:

 Out-Projekt: <input type= "checkbox" id= "OUT"> <br> <br>
 <button  class = "buttonz" onclick = "berechnung()">Berechnen </button>          

<script>
 function berechnung() {
 var OUT = parseInt(document.getElementById("OUT").checked);

if( checkbox.checked == true){ code}
 else { code }
}
</script>

For some reason, it does not work. I read other topics regarding this but found nothing suitable. Hope someone can help