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# Q914 How can I calculate the week number of the current date?

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The following will display the week number of the current date, and can be adapted to display the week number of any date:

```<script type="text/javascript" language="JavaScript"><!--
function y2k(number) { return (number < 1000) ? number + 1900 : number; }

function getWeek(year,month,day) {
var when = new Date(year,month,day);
var newYear = new Date(year,0,1);
var offset = 7 + 1 - newYear.getDay();
if (offset == 8) offset = 1;
var daynum = ((Date.UTC(y2k(year),when.getMonth(),when.getDate(),0,0,0) - Date.UTC(y2k(year),0,1,0,0,0)) /1000/60/60/24) + 1;
var weeknum = Math.floor((daynum-offset+7)/7);
if (weeknum == 0) {
year--;
var prevNewYear = new Date(year,0,1);
var prevOffset = 7 + 1 - prevNewYear.getDay();
if (prevOffset == 2 || prevOffset == 8) weeknum = 53; else weeknum = 52;
}
return weeknum;
}

var now = new Date();
document.write('Week number = ' + getWeek(y2k(now.getYear()),now.getMonth(),now.getDate()));
//--></script>```

European alternative provided by by Ferry van Schaik"

```<script type="text/javascript" language="JavaScript"><!--
function y2k(number) { return (number < 1000) ? number + 1900 : number; }

function getWeek(year,month,day) {
var when = new Date(year,month,day);
var newYear = new Date(year,0,1);
var modDay = newYear.getDay();
if (modDay == 0) modDay=6; else modDay--;

var daynum = ((Date.UTC(y2k(year),when.getMonth(),when.getDate(),0,0,0) -
Date.UTC(y2k(year),0,1,0,0,0)) /1000/60/60/24) + 1;

if (modDay < 4 ) {
var weeknum = Math.floor((daynum+modDay-1)/7)+1;
}
else {
var weeknum = Math.floor((daynum+modDay-1)/7);
if (weeknum == 0) {
year--;
var prevNewYear = new Date(year,0,1);
var prevmodDay = prevNewYear.getDay();
if (prevmodDay == 0) prevmodDay = 6; else prevmodDay--;
if (prevmodDay < 4) weeknum = 53; else weeknum = 52;
}
}

return + weeknum;
}

var now = new Date();
document.write('Week number = ' +
getWeek(y2k(now.getYear()),now.getMonth(),now.getDate()));
//--></script>```

European alternative, submitted by Ferry van Schaik

```<script type="text/javascript" language="JavaScript"><!--
function y2k(number) { return (number < 1000) ? number + 1900 : number; }

function getWeek(year,month,day) {
var when = new Date(year,month,day);
var newYear = new Date(year,0,1);
var modDay = newYear.getDay();
if (modDay == 0) modDay=6; else modDay--;

var daynum = ((Date.UTC(y2k(year),when.getMonth(),when.getDate(),0,0,0) - Date.UTC(y2k(year),0,1,0,0,0)) /1000/60/60/24) + 1;

if (modDay < 4 ) {
var weeknum = Math.floor((daynum+modDay-1)/7)+1;
} else {
var weeknum = Math.floor((daynum+modDay-1)/7);
if (weeknum == 0) {
year--;
var prevNewYear = new Date(year,0,1);
var prevmodDay = prevNewYear.getDay();
if (prevmodDay == 0) prevmodDay = 6; else prevmodDay--;
if (prevmodDay < 4) weeknum = 53; else weeknum = 52;
}
}

return + weeknum;
}

var now = new Date();
document.write('Week number = ' +
getWeek(y2k(now.getYear()),now.getMonth(),now.getDate()));
//--></script>```