JS: looping function through checkbox array not counting properly

I want to validate the input on a series of checkboxes. There must be at least one checkbox selected, otherwise the user gets an alert to select one.However, the alert appears unless all of the checkboxes are selected.

I realize that the issue is how my for loop params are set, but I cannot gigure out how to fix it. PLEASE!!!! help me. Your input and direction is greatly appreciated. Oh, I am very familiar with MDN and the resources there, but they do not have the answer :).

for(var i=0;i<7;i++){
    if( !checkboxes[i].checked ){
        alert( 'You need to select at least one day!');
        checkboxes[i].focus();
        return false;
    }
}