I need to calculate the duration between two datetimes in JavaScript. I have tried this code:

var today = new Date();
var dd = today.getDate();
var mm = today.getMonth()+1; //January is 0!

var yyyy = today.getFullYear();
if(dd<10){dd='0'+dd} if(mm<10){mm='0'+mm} today = mm+'/'+dd+'/'+yyyy;  //Current Date
console.log("current date"+today);


var valuestart ="8:00 AM";
var valuestop = "4:00 PM";//$("select[name='timestop']").val();

//create date format          
var timeStart = new Date("01/01/2007 " + valuestart).getHours();
var timeEnd = new Date("01/01/2007 " + valuestop).getHours();

var hourDiff = timeEnd - timeStart;             
console.log("duration"+hourDiff);

From this, I am able to get Current Date and duration. But when I replace the date "01/01/2007" with the variable "today", I am getting the result as NaN. Please guide me in where I am wrong. Thanks in advance.

I need to calculate the duration between two datetimes in JavaScript. I have tried this code:

var today = new Date();
var dd = today.getDate();
var mm = today.getMonth()+1; //January is 0!

var yyyy = today.getFullYear();
if(dd<10){dd='0'+dd} if(mm<10){mm='0'+mm} today = mm+'/'+dd+'/'+yyyy;  //Current Date
console.log("current date"+today);


var valuestart ="8:00 AM";
var valuestop = "4:00 PM";//$("select[name='timestop']").val();

//create date format          
var timeStart = new Date("01/01/2007 " + valuestart).getHours();
var timeEnd = new Date("01/01/2007 " + valuestop).getHours();

var hourDiff = timeEnd - timeStart;             
console.log("duration"+hourDiff);

From this, I am able to get Current Date and duration. But when I replace the date "01/01/2007" with the variable "today", I am getting the result as NaN. Please guide me in where I am wrong. Thanks in advance.

• javascript
• datetime

• are you sure timeStart & timeEnd are valid dates? – A1rPun Commented Feb 4, 2014 at 14:04
• Show us the code that's not working. Right now 'today' is a Date object – Geoffrey Burdett Commented Feb 4, 2014 at 14:05
• Its correct in the above code.But when i change that into var timeStart=new Date(""+today+""+valuestart+"").getHours(); and similar in timeEnd, i am getting problem – user2247744 Commented Feb 4, 2014 at 14:06

6 Answers 6

You should work on the epoch milliseconds. The idea is to transform everything to the epoch millis representation, perform your calculations, then go back to another format if needed.

There are many articles on the subject:

• Get the time difference between two datetimes
• http://www.htmlgoodies./html5/javascript/calculating-the-difference-between-two-dates-in-javascript.html#fbid=AojoSIQKaAL

Try this :

        var today = new Date();
        var dd = today.getDate();
        var mm = today.getMonth()+1; //January is 0!

        var yyyy = today.getFullYear();
        if(dd<10){dd='0'+dd} if(mm<10){mm='0'+mm} today = dd+'/'+mm+'/'+yyyy;  //Current Date

        var valuestart ="8:00 AM";
        var valuestop = "4:00 PM";//$("select[name='timestop']").val();

        //create date format  
        var timeStart = new Date(today + " " + valuestart).getHours();
        var timeEnd = new Date(today + " " + valuestop).getHours();

        var hourDiff = timeEnd - timeStart;  
        alert("duration:"+hourDiff);

today is of Date type whereas "01/01/2007" is a string. Trying to concatenate a Date object with "8:00 AM" will not work. You will have to turn today variable into a string or use today.setHours(8)

Maybe It's a little bit late. I second the answer from Christophe Roussy. First, calculate the difference in UTC format, then turn the unit - hour. I think it's easier to understand and maintain. Here's the code

var date1 = new Date(`some_valid_start_date_format`);
var date2 = new Date(`some_end_start_date_format`);

var duration = date2.valueOf() - date1.valueOf(); // The unit is millisecond
var hourDiff = parseInt(duration / (60 * 60 * 1000)) // Turn the duration into hour format

I tried luxon and it's very handy:

Given dt1 and dt2 as ISO representation of date time,

luxon.DateTime.fromISO(dt1).diff(
  luxon.DateTime.fromISO(dt2),
  ['years', 'months', 'days', 'hours', 'minutes', 'seconds']
).values

Simple Solution

If your duration is guaranteed to be less than 24 hours and you want to display it to the user here is a very simple solution:

function formatDuration(millis) {
    return new Date(millis).toISOString().substring(11, 19);
}

console.log(formatDuration(59999));    // 00:00:59
console.log(formatDuration(3599999));  // 00:59:59
console.log(formatDuration(86399999)); // 23:59:59

Better Solution

function formatDuration(millis) {
    let date = new Date(millis);
    let parts = [];

    if (date.getUTCFullYear() > 1970) {
        let years = date.getUTCFullYear() - 1970;
        parts.push(years, pluralize(years, 'year'));
    }
    if (date.getUTCMonth() > 0) { // months start at zero
        let months = date.getUTCMonth();
        parts.push(months, pluralize(months, 'month'));
    }
    if (date.getUTCDate() > 1) {
        let days = date.getUTCDate() - 1;
        parts.push(days, pluralize(days, 'day'));
    }

    parts.push(date.toISOString().substring(11, 19));

    return parts.join(' ');
}

function pluralize(count, singular, plural) {
    return count === 1 ? singular : plural ?? `${singular}s`;
}

console.log(formatDuration(new Date('1970-01-01T00:00:59.999Z').getTime())); // 00:00:59
console.log(formatDuration(new Date('1970-01-01T00:59:59.999Z').getTime())); // 00:59:59
console.log(formatDuration(new Date('1970-01-01T23:59:59.999Z').getTime())); // 23:59:59
console.log(formatDuration(new Date('1970-01-31T23:59:59.999Z').getTime())); // 30 days 23:59:59
console.log(formatDuration(new Date('1970-12-01T23:59:59.999Z').getTime())); // 11 months 23:59:59
console.log(formatDuration(new Date('1970-12-31T23:59:59.999Z').getTime())); // 11 months 30 days 23:59:59
console.log(formatDuration(new Date('1971-01-01T23:59:59.999Z').getTime())); // 1 year 23:59:59
console.log(formatDuration(new Date('1971-01-31T23:59:59.999Z').getTime())); // 1 year 30 days 23:59:59
console.log(formatDuration(new Date('1971-12-01T23:59:59.999Z').getTime())); // 1 year 11 months 23:59:59
console.log(formatDuration(new Date('1971-12-31T23:59:59.999Z').getTime())); // 1 year 11 months 30 days 23:59:59

If you want to include the milliseconds use this substring instead:

.substring(11, 23) // 23:59:59.999

and for pleteness the JSDoc:

/**
 * Formats a number of milliseconds to `HH:mm:ss`.
 * For durations of 24h and longer, prefixes the number of years, months, days if any are at least 1.
 * Examples:
 * * `00:00:59`
 * * `00:59:59`
 * * `23:59:59`
 * * `30 days 23:59:59`
 * * `11 months 23:59:59`
 * * `11 months 30 days 23:59:59`
 * * `1 year 23:59:59`
 * * `1 year 30 days 23:59:59`
 * * `1 year 11 months 23:59:59`
 * * `1 year 11 months 30 days 23:59:59`
 * @param {number} millis milliseconds
 * @return {string} the time portion in ISO format (excluding milliseconds) i.e. 23:59:59
 */