How can I display the first day of a two week period based on the current date with?

Question

What I need to do is take the current date and determine the first day of a two week pay period based on today's date. The pay periods start on Saturday. So for example, today (12/30) falls under the pay period for 12/20. All I need to do with that information is display it as Dec 20 2014. Any suggestions?

Thanks

Can you add more details about what language/environment you're doing this under? The tag mentions both ASP and Javascript. — Dave Challis, Dec 30 '14 at 15:25
@DaveChallis I'm not sure how I got asp-classic in the tags. I am wanting to do it in JavaScript, so I removed the ASP tag. — B_Dubbyah, Dec 30 '14 at 15:28
When do the periods start from, e.g. does the first pay period start on the first Saturday of the year? — Rhumborl, Dec 30 '14 at 15:35
@Rhumborl Yes the first pay period starts on the first Saturday of the year. So this year the first pay period is 1/3/15. — B_Dubbyah, Dec 30 '14 at 15:51

score 0 · Accepted Answer · edited May 23 '17 at 12:07

Using the ideas here for working out the difference between two dates, you can do the following:

function calculatePeriodStart(targetDate) {
    
    // get first day of year
    var day1 = new Date(targetDate.getFullYear(), 0, 1);
    
    // move forward to first Saturday
    day1.setDate(7 - day1.getDay());

    //Get 2 weeks in milliseconds
    var two_weeks = 1000 * 60 * 60 * 24 * 14;
    
    // Calculate the difference in milliseconds
    var difference_ms = targetDate.getTime() - day1.getTime();
    
    // Convert back to fortnights
    var numFortnightsD = difference_ms/two_weeks;
    var numFortnights = Math.ceil(numFortnightsD);
    
    // handle if on a Saturday, so a new cycle
    if(numFortnightsD == numFortnights)
    {
        numFortnights++;
    }
    
    // add the number of fortnights
    // but take one off to get the current period
    day1.setDate(day1.getDate() + (numFortnights-1)*14);
    
    return day1;
}

// examples

console.log('-----');

// today
var today = new Date();
console.log(today + ' => ' + calculatePeriodStart(today) + ' (today)');

// just before midnight of new period
var today = new Date(2014, 11, 19, 23, 59, 59);
console.log(today + ' => ' + calculatePeriodStart(today) + ' (just before midnight of new period)');

// exactly on midnight of new period
today = new Date(2014, 11, 20);
console.log(today + ' => ' + calculatePeriodStart(today) + ' (exactly on midnight of new period)');

// just after midnight of new period
today = new Date(2014, 11, 20, 0, 0, 1)
console.log(today + ' => ' + calculatePeriodStart(today) + ' (just after midnight of new period)');

// just after midnight of new period next year
today = new Date(2015, 11, 19, 0, 0, 1);
console.log(today + ' => ' + calculatePeriodStart(today) + ' (just after midnight of new period next year)');

// earlier than 1st period in year
today = new Date(2014, 0, 2);
console.log(today + ' => ' + calculatePeriodStart(today) + ' (earlier than 1st period in year)');

calculatePeriodStart() will return a Date object. To format the date for display, you can use this answer.

This worked great. I had to adjust it a little bit, as I actually was a little off on how the pay periods works. Thanks a bunch. — B_Dubbyah, Dec 30 '14 at 20:16

How can I display the first day of a two week period based on the current date with?

1 Answers1