freenick,
<!DOCTYPE HTML>
<html>
<head>
<title>Untitled</title>
<meta charset="utf-8">
<style type="text/css">
</style>
</head>
<body>
<input type="checkbox" class="day" value="1">ПН<br>
<input type="checkbox" class="day" value="2">ВТ<br>
<input type="checkbox" class="day" value="3">СР<br>
<input type="checkbox" class="day" value="4">ЧТ<br>
<input type="checkbox" class="day" value="5">ПТ<br>
<input type="checkbox" class="day" value="6">СБ<br>
<input type="checkbox" class="day" value="0">ВС<br>
<input type="button" name="save" id="save" value="GO" ><br>
<script>
window.addEventListener('DOMContentLoaded', function() {
var save = document.querySelector('#save');
save.addEventListener('click', function() {
var days = document.querySelectorAll('.day:checked'),
sum = 0,
arr = [].map.call( days, function(sel) {
return +sel.value
});
var today = new Date();
var futureDay = new Date(2016, 1, 16);
for (; today<futureDay; ) {
if (!!~arr.indexOf(today.getDay())) sum++;
today.setDate(1 + today.getDate())
}
alert(sum)
});
});
</script>
</body>
</html>