Add Working Days to a Date Using JavaScript

Question

How can I use JavaScript to add working days (i.e. Mon - Friday) automatically adding weekends where necessary?

So if I were to add 5 working days to today (Tue. 22nd Nov. 2016) the result should be "Tue. 29th Nov. 2016" and not "Sun. 27th Nov. 2016".

Answer 1

Update Dec 2023

In general, there can be 2 methods to add working (business) days to a particular date:

Method 1. Workdays to Calendar Days Conversion

Under this method, the working days to be added are first converted to calendar days based on 2 additional days (i.e. weekend days) for every 5 working days. The resulting calendar days are then added to the date to arrive at the working date.

This assumes 2 weekend days per week that are consecutive (i.e. Sat & Sun, Fri & Sat, or Thu & Fri).

This method is not as simple as Method 2 (see below) for subtraction, adapting to other locales' weekends, using non-consecutive weekend days, or excluding holiday days.

The code will also need to cater for starting dates and resulting dates falling on weekends and corrections be made for that. This will increase code complexity for negative days count and for weekends that are non-consecutive days (such as weekends that are Friday and Sunday but not Saturday).

Method 2. Using a loop to skip weekend days (a for or while loop)

This method is simple, clean, easy to understand, and permits easy adaption for the following:

1. Subtracting workdays from the given date.
2. Non-consecutive weekend days.
3. Simple implementation of other locales weekends (either 2 or 1 day weekends).
4. Simple adaption to exclude holiday days. This is because each date is tested for being a weekend or not.

But Method 2 will be slower than Method 1?

In real-life use, the number of work days to be added to (or subtracted from) a particular date will not be hundreds of thousands or millions of work days.

A full year has 261 working days (assuming 2 days weekend) or 313 days assuming a 1 day weekend.

In practise, you will not need to add such a large number of work days !!

Some practical examples would be:

1. Find the working days of a calendar year.
2. Generate a calendar for a year with work days.
3. Calculate the workdays for salary payments.

The above examples would need to only work with 100's of workdays and not millions of days.

In its basic form for adding work days, Method 2 is a one-line code using a while loop.

while (days) ![6,0].includes(date.getUTCDay(date.setUTCDate(date.getUTCDate()+1))) && days--;

The while loop works as follows:

//    1. let days => to be workdays to be added
//    2. let date => to be the start date
//    3. start while loop
// |->4. if days==0 return date [exit]
// |  5. get next date (date +=1)
// |  6. is the day a weekend? (day number in the array?)
// |  7. if not a weekend decrement days (days--)
// |<-8. loop again (step 4)

Notwithstanding the above, even if adding (say) 100 years’ worth of work days which is 261 x 100 = 26,100 work days using Method 2 as shown in the example below takes on average less than 15 milliseconds.

Here is an example with a test to add over 26,000 work days (100 years) !! with the resulting approximate execution time.

function addWorkDays(date, days) {
while (days) ![6,0].includes(date.getUTCDay(date.setUTCDate(date.getUTCDate()+1))) && days--;
return date;
}

//========= Test to add 100 years of working days ==========
let workdays = 261*100;  // 100 years of working days !!
const t0 = performance.now();
console.log(addWorkDays(new Date("2023-12-03"),workdays));  // date => 2123-12-17
const t1 = performance.now();
console.log(`Adding 100 years of work days took ${(t1-t0).toFixed(2)} milliseconds.`);

The above function assumes that weekend days are Saturday and Sunday days [6,0].

You can change that (the numbers in the array) to other weekend days say Friday and Saturday [5,6] as used in the Middle East and North Africa or just a one-day weekend like Sunday [0] as used in India, Philippines, etc.

Subtracting Work Days from a Date

The above simple one-line function cannot “subtract” workdays from a given date.

To do that we add the following 2 lines:

 let dir  = days<0?-1:1;  // if negative days then decrement
 days = Math.abs(days);   // days always positive integer

So, if the number of days is negative, instead of increasing the date by 1 (the next day), we use the variable dir which is -1 to decrease the date (previous day).

The revised function to add and subtract working dates from a date becomes:

function addWorkDays(date, days) {
let dir  = days<0?-1:1;
    days = Math.abs(days);
while (days) ![6,0].includes(date.getUTCDay(date.setUTCDate(date.getUTCDate()+dir))) && days--;
return date;
}

//===== test examples ====
console.log(addWorkDays(new Date("2023-12-03"),-10));   // 2023-11-20
console.log(addWorkDays(new Date("2023-12-03"),-20));   // 2023-11-06

Create a function that mimics MS Excel WORKDAY.INTL to add and subtract workdays for different locales

The above function can be improved by making it cater for weekends of different locales (other countries) so that it can mimic and produce the same results as used by MS Excel WORDAY and WORKDAY.INTL functions.

We can do that by passing the weekends as a parameter to the function either as an array of weekend days, or by finding the weekend information from the Intl.Locale constructor or by allowing both ways.

As the Intl.Locale(locale).weekInfo.weekend returns Sunday as day number 7 rather than 0, we will need to correct for that by changing 7 to 0 (if any) so that the getDay() method of Date understands it.

The short function below can now handle the addition and subtraction of workdays as well as handling other locales’ weekends.

The function now can accept other weekend locales (default is en-US, i.e. Sat and Sun).

Locales can be passed either as locale identifier strings (like 'en-US') or as an array of weekend days (like [4,5]).

The output produced will be identical to that produced by MS Excel WORDAY and WORKDAY.INTL functions, and it is fast.

function addWorkDays(date, days, locale="en-US") {
date=new Date(date);               // allow date to be given as ISO string
let w = Array.isArray(locale)?locale:new Intl.Locale(locale).weekInfo.weekend,
 dir  = days<0?-1:1;               // if negative days then decrement
 days = Math.abs(days);            // days always positive integer
 w.at(-1)==7 && (w[w.length-1]=0); // correct Sunday day from 7 to 0
while (days) !w.includes(date.getUTCDay(date.setUTCDate(date.getUTCDate()+dir))) && days--;
return date;
}

//======== test examples ========
console.log(addWorkDays("2023-12-03",10));          // 2023-12-15
console.log(addWorkDays("2023-12-03",10,"en-IN"));  // 2023-12-14
console.log(addWorkDays("2023-12-03",10,"ar-QA"));  // 2023-12-17
console.log(addWorkDays("2023-12-03",10,[5,6]));    // 2023-12-17
console.log(addWorkDays("2023-12-03",-10));         // 2023-11-20
console.log(addWorkDays("2023-12-03",-10,"en-IN")); // 2023-11-22
console.log(addWorkDays("2023-12-03",-10,"ar-QA")); // 2023-11-19
console.log(addWorkDays("2023-12-03",-10,[5,6]));   // 2023-11-19

Testing for Correct Results

The following tests have been confirmed with MS Excel WORKDAY.INTL function both for positive and negative days and with various locales. Using small and large workdays.

function addWorkDays(date, days, locale= "en-US") {
date=new Date(date);
let w = Array.isArray(locale)?locale:new Intl.Locale(locale).weekInfo.weekend,
 dir  = days<0?-1:1;
 days = Math.abs(days);
 w.at(-1)==7 && (w[w.length-1]=0);
while (days) !w.includes(date.getUTCDay(date.setUTCDate(date.getUTCDate()+dir))) && days--;
return date;
}

//=========================================
//             Test Cases
//=========================================

//========================================
// Test with Sat-Sun as weekend default
// uses locale 'en-US' for USA by default
//========================================

var r=0; // test tracker
r |=test(1,"2023-11-27",1,new Date("2023-11-28"));
r |=test(2,"2023-11-27",2,new Date("2023-11-29"));
r |=test(3,"2023-11-27",3,new Date("2023-11-30"));
r |=test(4,"2023-11-27",4,new Date("2023-12-01"));
r |=test(5,"2023-11-27",5,new Date("2023-12-04"));
r |=test(6,"2023-11-27",6,new Date("2023-12-05"));
r |=test(7,"2023-11-27",7,new Date("2023-12-06"));
r |=test(8,"2023-11-27",8,new Date("2023-12-07"));
r |=test(9,"2023-11-27",9,new Date("2023-12-08"));
r |=test(10,"2023-12-02",1,new Date("2023-12-04"));
r |=test(11,"2023-12-02",2,new Date("2023-12-05"));
r |=test(12,"2023-12-02",3,new Date("2023-12-06"));
r |=test(13,"2023-12-03",1,new Date("2023-12-04"));
r |=test(14,"2023-12-03",2,new Date("2023-12-05"));
r |=test(15,"2021-02-01",2,new Date("2021-02-03"));
r |=test(16,"2021-02-01",3,new Date("2021-02-04"));
r |=test(17,"2021-02-01",4,new Date("2021-02-05"));
r |=test(18,"2021-02-01",5,new Date("2021-02-08"));
r |=test(19,"2021-02-01",365,new Date("2022-06-27"));
r |=test(20,"2021-02-01",100,new Date("2021-06-21"));
r |=test(21,"2021-02-01",20000,new Date("2097-09-30"));
r |=test(24,"2023-12-01",-1,new Date("2023-11-30"));
r |=test(25,"2023-12-01",-2,new Date("2023-11-29"));
r |=test(26,"2023-12-01",-3,new Date("2023-11-28"));
r |=test(27,"2023-12-01",-4,new Date("2023-11-27"));
r |=test(28,"2023-12-01",-365,new Date("2022-07-08"));
r |=test(29,"2023-12-01",-100,new Date("2023-07-14"));
r |=test(30,"2023-12-01",-999,new Date("2020-02-03"));
r |=test(31,"2023-12-02",-1,new Date("2023-12-01"));
r |=test(32,"2023-12-02",-2,new Date("2023-11-30"));
r |=test(33,"2023-12-02",-3,new Date("2023-11-29"));
r |=test(34,"2023-12-02",-4,new Date("2023-11-28"));
r |=test(35,"2023-12-02",-365,new Date("2022-07-11"));
r |=test(36,"2023-12-02",-100,new Date("2023-07-17"));
r |=test(37,"2023-12-02",-999,new Date("2020-02-04"));
r |=test(38,"2023-12-03",-1,new Date("2023-12-01"));
r |=test(39,"2023-12-03",-2,new Date("2023-11-30"));
r |=test(40,"2023-12-03",-3,new Date("2023-11-29"));
r |=test(41,"2023-12-03",-4,new Date("2023-11-28"));
r |=test(42,"2023-12-04",-1,new Date("2023-12-01"));
r |=test(43,"2023-12-04",-2,new Date("2023-11-30"));
r |=test(44,"2023-12-04",-3,new Date("2023-11-29"));
r |=test(45,"2023-12-04",-4,new Date("2023-11-28"));
r |=test(46,"2023-12-04",-5,new Date("2023-11-27"));
r |=test(47,"2023-12-04",-6,new Date("2023-11-24"));
r |=test(48,"2023-12-04",-7,new Date("2023-11-23"));
r |=test(49,"2023-12-04",-8,new Date("2023-11-22"));

if (r==0) console.log("✅ (Sat-Sun) Weekend Passed.");

//========================================
// Test with Fri-Sat as weekend
// use example locale 'ar-SA' for Saudi Arabia
//========================================
var r=0; // test tracker
var locale="ar-SA";
r |=test(1,"2023-11-27",1,new Date("2023-11-28"),locale);
r |=test(2,"2023-11-27",0,new Date("2023-11-27"),locale);
r |=test(3,"2023-12-02",0,new Date("2023-12-02"),locale);
r |=test(4,"2023-12-01",0,new Date("2023-12-01"),locale);
r |=test(5,"2023-11-27",2,new Date("2023-11-29"),locale);
r |=test(6,"2023-11-27",3,new Date("2023-11-30"),locale);
r |=test(7,"2023-11-27",4,new Date("2023-12-03"),locale);
r |=test(8,"2023-11-27",5,new Date("2023-12-04"),locale);
r |=test(9,"2023-11-27",6,new Date("2023-12-05"),locale);
r |=test(10,"2023-11-27",7,new Date("2023-12-06"),locale);
r |=test(11,"2023-11-27",8,new Date("2023-12-07"),locale);
r |=test(12,"2023-11-27",9,new Date("2023-12-10"),locale);
r |=test(13,"2023-12-02",1,new Date("2023-12-03"),locale);
r |=test(14,"2023-12-02",2,new Date("2023-12-04"),locale);
r |=test(15,"2023-12-02",3,new Date("2023-12-05"),locale);
r |=test(16,"2023-12-03",1,new Date("2023-12-04"),locale);
r |=test(17,"2023-12-03",2,new Date("2023-12-05"),locale);
r |=test(18,"2021-02-01",2,new Date("2021-02-03"),locale);
r |=test(19,"2021-02-01",3,new Date("2021-02-04"),locale);
r |=test(20,"2021-02-01",4,new Date("2021-02-07"),locale);
r |=test(21,"2021-02-01",5,new Date("2021-02-08"),locale);
r |=test(22,"2021-02-01",365,new Date("2022-06-27"),locale);
r |=test(23,"2021-02-01",100,new Date("2021-06-21"),locale);
r |=test(24,"2021-02-01",20000,new Date("2097-09-30"),locale);
r |=test(25,"2023-12-01",-1,new Date("2023-11-30"),locale);
r |=test(26,"2023-12-01",-2,new Date("2023-11-29"),locale);
r |=test(27,"2023-12-01",-3,new Date("2023-11-28"),locale);
r |=test(28,"2023-12-01",-4,new Date("2023-11-27"),locale);
r |=test(29,"2023-12-01",-365,new Date("2022-07-10"),locale);
r |=test(30,"2023-12-01",-100,new Date("2023-07-16"),locale);
r |=test(31,"2023-12-01",-999,new Date("2020-02-03"),locale);
r |=test(32,"2023-12-02",-1,new Date("2023-11-30"),locale);
r |=test(33,"2023-12-02",-2,new Date("2023-11-29"),locale);
r |=test(34,"2023-12-02",-3,new Date("2023-11-28"),locale);
r |=test(35,"2023-12-02",-4,new Date("2023-11-27"),locale);
r |=test(36,"2023-12-02",-365,new Date("2022-07-10"),locale);
r |=test(37,"2023-12-02",-100,new Date("2023-07-16"),locale);
r |=test(38,"2023-12-02",-999,new Date("2020-02-03"),locale);
r |=test(39,"2023-12-03",-1,new Date("2023-11-30"),locale);
r |=test(40,"2023-12-03",-2,new Date("2023-11-29"),locale);
r |=test(41,"2023-12-03",-3,new Date("2023-11-28"),locale);
r |=test(42,"2023-12-03",-4,new Date("2023-11-27"),locale);
r |=test(43,"2023-12-04",-1,new Date("2023-12-03"),locale);
r |=test(44,"2023-12-04",-2,new Date("2023-11-30"),locale);
r |=test(45,"2023-12-04",-3,new Date("2023-11-29"),locale);
r |=test(46,"2023-12-04",-4,new Date("2023-11-28"),locale);
r |=test(47,"2023-12-04",-5,new Date("2023-11-27"),locale);
r |=test(48,"2023-12-04",-6,new Date("2023-11-26"),locale);
r |=test(49,"2023-12-04",-7,new Date("2023-11-23"),locale);
r |=test(50,"2023-12-04",-8,new Date("2023-11-22"),locale);
if (r==0) console.log("✅ (Fri-Sat) Weekend Passed.");


//========================================
// Test with Thu-Fri as weekend
// use example locale 'ps-AF' for Afghanistan
//========================================
var r=0; // test tracker
var locale="ps-AF";
r |=test(1,"2023-11-27",1,new Date("2023-11-28"),locale);
r |=test(2,"2023-11-27",0,new Date("2023-11-27"),locale);
r |=test(3,"2023-11-30",0,new Date("2023-11-30"),locale);
r |=test(4,"2023-12-01",0,new Date("2023-12-01"),locale);
r |=test(5,"2023-11-27",2,new Date("2023-11-29"),locale);
r |=test(6,"2023-11-27",3,new Date("2023-12-02"),locale);
r |=test(7,"2023-11-27",4,new Date("2023-12-03"),locale);
r |=test(8,"2023-11-27",5,new Date("2023-12-04"),locale);
r |=test(9,"2023-11-27",6,new Date("2023-12-05"),locale);
r |=test(10,"2023-11-27",7,new Date("2023-12-06"),locale);
r |=test(11,"2023-11-27",8,new Date("2023-12-09"),locale);
r |=test(12,"2023-11-27",9,new Date("2023-12-10"),locale);
r |=test(13,"2023-12-02",1,new Date("2023-12-03"),locale);
r |=test(14,"2023-12-02",2,new Date("2023-12-04"),locale);
r |=test(15,"2023-12-02",3,new Date("2023-12-05"),locale);
r |=test(16,"2023-12-03",1,new Date("2023-12-04"),locale);
r |=test(17,"2023-12-03",2,new Date("2023-12-05"),locale);
r |=test(18,"2021-02-01",2,new Date("2021-02-03"),locale);
r |=test(19,"2021-02-01",3,new Date("2021-02-06"),locale);
r |=test(20,"2021-02-01",4,new Date("2021-02-07"),locale);
r |=test(21,"2021-02-01",5,new Date("2021-02-08"),locale);
r |=test(22,"2021-02-01",365,new Date("2022-06-27"),locale);
r |=test(23,"2021-02-01",100,new Date("2021-06-21"),locale);
r |=test(24,"2021-02-01",20000,new Date("2097-09-30"),locale);
r |=test(25,"2021-02-01",-1,new Date("2021-01-31"),locale);
r |=test(26,"2021-02-01",-2,new Date("2021-01-30"),locale);
r |=test(27,"2021-02-01",-3,new Date("2021-01-27"),locale);
r |=test(28,"2021-02-01",-4,new Date("2021-01-26"),locale);
r |=test(29,"2021-02-01",-365,new Date("2019-09-09"),locale);
r |=test(30,"2021-02-01",-100,new Date("2020-09-14"),locale);
r |=test(31,"2021-02-01",-999,new Date("2017-04-04"),locale);
if (r==0) console.log("✅ (Thu-Fri) Weekend Passed.");

//========================================
// Test with Fri as weekend
// use example locale 'fa-IR' for Iran
//========================================
var locale="fa-IR";
var r=0;
r |=test(1,"2023-11-27",1,new Date("2023-11-28"),locale);
r |=test(2,"2023-11-27",2,new Date("2023-11-29"),locale);
r |=test(3,"2023-11-27",3,new Date("2023-11-30"),locale);
r |=test(4,"2023-11-27",4,new Date("2023-12-02"),locale);
r |=test(5,"2023-11-27",5,new Date("2023-12-03"),locale);
r |=test(6,"2023-11-27",6,new Date("2023-12-04"),locale);
r |=test(7,"2023-11-27",7,new Date("2023-12-05"),locale);
r |=test(8,"2023-11-27",8,new Date("2023-12-06"),locale);
r |=test(9,"2023-11-27",9,new Date("2023-12-07"),locale);
r |=test(10,"2023-12-02",1,new Date("2023-12-03"),locale);
r |=test(11,"2023-12-02",2,new Date("2023-12-04"),locale);
r |=test(12,"2023-12-02",3,new Date("2023-12-05"),locale);
r |=test(13,"2023-12-03",1,new Date("2023-12-04"),locale);
r |=test(14,"2023-12-03",2,new Date("2023-12-05"),locale);
r |=test(15,"2021-02-01",2,new Date("2021-02-03"),locale);
r |=test(16,"2021-02-01",3,new Date("2021-02-04"),locale);
r |=test(17,"2021-02-01",4,new Date("2021-02-06"),locale);
r |=test(18,"2021-02-01",5,new Date("2021-02-07"),locale);
r |=test(19,"2021-02-01",365,new Date("2022-04-03"),locale);
r |=test(20,"2021-02-01",100,new Date("2021-05-29"),locale);
r |=test(21,"2021-02-01",20000,new Date("2084-12-20"),locale);
r |=test(22,"2021-02-01",-1,new Date("2021-01-31"),locale);
r |=test(23,"2021-02-01",-2,new Date("2021-01-30"),locale);
r |=test(24,"2021-02-01",-3,new Date("2021-01-28"),locale);
r |=test(25,"2021-02-01",-4,new Date("2021-01-27"),locale);
r |=test(26,"2021-02-01",-365,new Date("2019-12-03"),locale);
r |=test(27,"2021-02-01",-100,new Date("2020-10-07"),locale);
r |=test(28,"2021-02-01",-999,new Date("2017-11-23"),locale);

if (r==0) console.log("✅ (Friday only)   Weekend Passed.");

//========================================
// Test with Sunday as weekend
// use example locale 'en-IN' for India
//========================================
var locale="en-IN";
var r=0;
r |=test(1,"2023-11-27",1,new Date("2023-11-28"),locale);
r |=test(2,"2023-11-27",2,new Date("2023-11-29"),locale);
r |=test(3,"2023-11-27",3,new Date("2023-11-30"),locale);
r |=test(4,"2023-11-27",4,new Date("2023-12-01"),locale);
r |=test(5,"2023-11-27",5,new Date("2023-12-02"),locale);
r |=test(6,"2023-11-27",6,new Date("2023-12-04"),locale);
r |=test(7,"2023-11-27",7,new Date("2023-12-05"),locale);
r |=test(8,"2023-11-27",8,new Date("2023-12-06"),locale);
r |=test(9,"2023-11-27",9,new Date("2023-12-07"),locale);
r |=test(10,"2023-12-02",1,new Date("2023-12-04"),locale);
r |=test(11,"2023-12-02",2,new Date("2023-12-05"),locale);
r |=test(12,"2023-12-02",3,new Date("2023-12-06"),locale);
r |=test(13,"2023-12-03",1,new Date("2023-12-04"),locale);
r |=test(14,"2023-12-03",2,new Date("2023-12-05"),locale);
r |=test(15,"2021-02-01",2,new Date("2021-02-03"),locale);
r |=test(16,"2021-02-01",3,new Date("2021-02-04"),locale);
r |=test(17,"2021-02-01",4,new Date("2021-02-05"),locale);
r |=test(18,"2021-02-01",5,new Date("2021-02-06"),locale);
r |=test(19,"2021-02-01",365,new Date("2022-04-02"),locale);
r |=test(20,"2021-02-01",100,new Date("2021-05-28"),locale);
r |=test(21,"2021-02-01",20000,new Date("2084-12-20"),locale);
r |=test(22,"2021-02-01",-1,new Date("2021-01-30"),locale);
r |=test(23,"2021-02-01",-2,new Date("2021-01-29"),locale);
r |=test(24,"2021-02-01",-3,new Date("2021-01-28"),locale);
r |=test(25,"2021-02-01",-4,new Date("2021-01-27"),locale);
r |=test(26,"2021-02-01",-365,new Date("2019-12-03"),locale);
r |=test(27,"2021-02-01",-100,new Date("2020-10-07"),locale);
r |=test(28,"2021-02-01",-999,new Date("2017-11-23"),locale);

if (r==0) console.log("✅ (Sunday only)   Weekend Passed.");

//========================================
// Test with Sat as weekend
// use example array day 6 [6]
//========================================
var locale=[6];
var r=0;
r |=test(1,"2023-11-27",1,new Date("2023-11-28"),locale);
r |=test(2,"2023-11-27",2,new Date("2023-11-29"),locale);
r |=test(3,"2023-11-27",3,new Date("2023-11-30"),locale);
r |=test(4,"2023-11-27",4,new Date("2023-12-01"),locale);
r |=test(5,"2023-11-27",5,new Date("2023-12-03"),locale);
r |=test(6,"2023-11-27",6,new Date("2023-12-04"),locale);
r |=test(7,"2023-11-27",7,new Date("2023-12-05"),locale);
r |=test(8,"2023-11-27",8,new Date("2023-12-06"),locale);
r |=test(9,"2023-11-27",9,new Date("2023-12-07"),locale);
r |=test(10,"2023-12-02",1,new Date("2023-12-03"),locale);
r |=test(11,"2023-12-02",2,new Date("2023-12-04"),locale);
r |=test(12,"2023-12-02",3,new Date("2023-12-05"),locale);
r |=test(13,"2023-12-03",1,new Date("2023-12-04"),locale);
r |=test(14,"2023-12-03",2,new Date("2023-12-05"),locale);
r |=test(15,"2021-02-01",2,new Date("2021-02-03"),locale);
r |=test(16,"2021-02-01",3,new Date("2021-02-04"),locale);
r |=test(17,"2021-02-01",4,new Date("2021-02-05"),locale);
r |=test(18,"2021-02-01",5,new Date("2021-02-07"),locale);
r |=test(19,"2021-02-01",365,new Date("2022-04-03"),locale);
r |=test(20,"2021-02-01",100,new Date("2021-05-28"),locale);
r |=test(21,"2021-02-01",20000,new Date("2084-12-20"),locale);
r |=test(22,"2021-02-01",-1,new Date("2021-01-31"),locale);
r |=test(23,"2021-02-01",-2,new Date("2021-01-29"),locale);
r |=test(24,"2021-02-01",-3,new Date("2021-01-28"),locale);
r |=test(25,"2021-02-01",-4,new Date("2021-01-27"),locale);
r |=test(26,"2021-02-01",-365,new Date("2019-12-03"),locale);
r |=test(27,"2021-02-01",-100,new Date("2020-10-07"),locale);
r |=test(28,"2021-02-01",-999,new Date("2017-11-23"),locale);

if (r==0) console.log("✅ (Saturday only) Weekend Passed.");

//=====================================
// Tester Function
//=====================================
function test(test,startDate,wDays,should,locale) {
let result = addWorkDays(startDate,wDays,locale);
if (""+result !== ""+should) {
    console.log(`${test}. Output   : ${result}\n    Should be: ${should}`);return 1;
    }
}

Answer 2

An even simpler solution in pure JS using an array to know how many days to add to the current day of the week. Sunday is the first element in the array and you add 5 business days to get Friday. The weekdays all add 7 days to come up with the same day next week. Saturday adds 6 days to come up with Friday.

const daysToAddForFiveBusinessDays = [5,7,7,7,7,7,6]
function date5BusinessDays (startDate) {
    return new Date(startDate.setDate(startDate.getDate() + daysToAddForFiveBusinessDays [startDate.getDay()]));
}

I am going to use this style to find 3 working days in the future, and that code is listed below. For Sunday Monday and Tuesday you just add 3 business days, on Wednesday through Friday you add 5 days to get 3 business days, and on Saturday you need to add 4 days to get 3 business days.

const daysToAddForThreeBusinessDays = [3,3,3,5,5,5,4]
function date3BusinessDays(startDate) {
    return new Date(startDate.setDate(startDate.getDate() + daysToAddForThreeBusinessDays[startDate.getDay()]));
}

const daysToAddForFiveBusinessDays = [5,7,7,7,7,7,6]
const daysToAddForThreeBusinessDays = [3,3,3,5,5,5,4]

function fiveBusinessDaysFrom (startDate) {
    return new Date(startDate.setDate(startDate.getDate() + daysToAddForFiveBusinessDays [startDate.getDay()]));
}

function threeBusinessDaysFrom(startDate) {
    return new Date(startDate.setDate(startDate.getDate() + daysToAddForThreeBusinessDays[startDate.getDay()]));
}

console.log("five business days from today is " + fiveBusinessDaysFrom(new Date()))
console.log("three business days from today is " + threeBusinessDaysFrom(new Date()))

Answer 3

This is my simplyest final solution for me:

function addWorkDays(startDate, daysToAdd) {
  let dw=startDate.getDay(); //* see note
  startDate.setDate(startDate.getDate()-((dw==6)?1:(dw==0)?2:0)); //*
  var avance = 2 * Math.floor(daysToAdd / 5); //add 2 days for each 5 workdays
  var exceso = (daysToAdd % 5) + startDate.getDay() ;
  if (exceso>=6) avance +=2 ; 
  startDate.setDate(startDate.getDate() + daysToAdd + avance);
  return startDate;
}

// If used only with business day dates, the first two lines are not required

Answer 4

If it's for adding a few days, not thousands of days, then this is easier and more readable:

const currentDate = new Date('2021-11-18');
console.log(currentDate.toString()); // "Thu Nov 18 2021 00:00:00 GMT+0000"

const numToAdd = 5;

for (let i = 1; i <= numToAdd; i++) {
  currentDate.setDate(currentDate.getDate() + 1);
  if (currentDate.getDay() === 6) {
    currentDate.setDate(currentDate.getDate() + 2);
  }
  else if (currentDate.getDay() === 0) {
    currentDate.setDate(currentDate.getDate() + 1);
  }
}

console.log(currentDate.toString()); // "Thu Nov 25 2021 00:00:00 GMT+0000"

Answer 5

Updated above script to also subtract workdays if negative days are given...

function addWorkDays(startDate, days) {
    var isAddingDays = (days > 0);
    var isDaysToAddMoreThanWeek = (days > 5 || days < -5);

    if (isNaN(days)) {
        console.log("Value provided for \"days\" was not a number");
        return
    }
    if (!(startDate instanceof Date)) {
        console.log("Value provided for \"startDate\" was not a Date object");
        return
    }
    var dow = startDate.getDay();
    var daysToAdd = parseInt(days);

    if ((dow === 0 && isAddingDays) || (dow === 6 && !isAddingDays)) {
        daysToAdd = daysToAdd + (1 * (isAddingDays ? 1 : -1));
    } else if ((dow === 6 && isAddingDays) || (dow === 0 && !isAddingDays)) {
        daysToAdd = daysToAdd + (2 * (isAddingDays ? 1 : -1));
    }

    if (isDaysToAddMoreThanWeek) {
        daysToAdd = daysToAdd + (2 * (Math.floor(days / 5)));

        if (days % 5 != 0)
            daysToAdd = daysToAdd + (2 * (isAddingDays ?  -1 : 1));
    }

    startDate.setDate(startDate.getDate() + daysToAdd);
    var newDate = moment(startDate).format('MM/DD/YYYY');
    return newDate;
}

Answer 6

It is possible to use Date's setDate function (in combination with getDate) to add days onto a date i.e. -

var myDate = new Date(); // Tue 22/11/2016
myDate.setDate(myDate.getDate() + 3); // Fri 25/11/2016

So once you've calculated the number of weekend days within the workdays period you can add that and the required number of workdays to the start date to get the final date.

This function should work though obviously this will not take account of national holidays -

function addWorkDays(startDate, days) {
    if(isNaN(days)) {
        console.log("Value provided for \"days\" was not a number");
        return
    }
    if(!(startDate instanceof Date)) {
        console.log("Value provided for \"startDate\" was not a Date object");
        return
    }
    // Get the day of the week as a number (0 = Sunday, 1 = Monday, .... 6 = Saturday)
    var dow = startDate.getDay();
    var daysToAdd = parseInt(days);
    // If the current day is Sunday add one day
    if (dow == 0)
        daysToAdd++;
    // If the start date plus the additional days falls on or after the closest Saturday calculate weekends
    if (dow + daysToAdd >= 6) {
        //Subtract days in current working week from work days
        var remainingWorkDays = daysToAdd - (5 - dow);
        //Add current working week's weekend
        daysToAdd += 2;
        if (remainingWorkDays > 5) {
            //Add two days for each working week by calculating how many weeks are included
            daysToAdd += 2 * Math.floor(remainingWorkDays / 5);
            //Exclude final weekend if remainingWorkDays resolves to an exact number of weeks
            if (remainingWorkDays % 5 == 0)
                daysToAdd -= 2;
        }
    }
    startDate.setDate(startDate.getDate() + daysToAdd);
    return startDate;
}

//And use it like so (months are zero based)
var today = new Date(2016, 10, 22);
today = addWorkDays(today, 5); // Tue Nov 29 2016 00:00:00 GMT+0000 (GMT Standard Time)

It could also be added to the Date prototype -

Date.prototype.addWorkDays = function (days) {
    if(isNaN(days)) {
        console.log("Value provided for \"days\" was not a number");
        return
    }

    // Get the day of the week as a number (0 = Sunday, 1 = Monday, .... 6 = Saturday)
    var dow = this.getDay();
    var daysToAdd = parseInt(days);
    // If the current day is Sunday add one day
    if (dow == 0) {
        daysToAdd++;
    }
    // If the start date plus the additional days falls on or after the closest Saturday calculate weekends
    if (dow + daysToAdd >= 6) {
        //Subtract days in current working week from work days
        var remainingWorkDays = daysToAdd - (5 - dow);
        //Add current working week's weekend
        daysToAdd += 2;
        if (remainingWorkDays > 5) {
            //Add two days for each working week by calculating how many weeks are included
            daysToAdd += 2 * Math.floor(remainingWorkDays / 5);
            //Exclude final weekend if the remainingWorkDays resolves to an exact number of weeks
            if (remainingWorkDays % 5 == 0)
                daysToAdd -= 2;
        }
    }
    this.setDate(this.getDate() + daysToAdd);
};

//And use it like so (months are zero based)
var today = new Date(2016, 10, 22)
today.addWorkDays(5); // Tue Nov 29 2016 00:00:00 GMT+0000 (GMT Standard Time)

Answer 7

const date = new Date('2000-02-02')
const daysToAdd = mapToWorkdays(date, 37)

date.setUTCDate(date.getUTCDate() + daysToAdd)

console.log( date.toISOString().split('T')[0] )
// prints 2000-03-24

/**
 * @param {Date} date starting date
 * @param {number} add number of workdays to add
 * @return {number} total number of days to add to reach correct date
 */
function mapToWorkdays(date, add) {
  const wd = weekday(date)
  
  let r = Math.trunc(add / 5) * 2
  const rem = add % 5

  if (wd > 4) r += (6-wd)
  else if (wd+rem > 4) r += 2

  return add + r
}

/**
 * @param {Date} date
 * @return {number} day of the week in range of 0..6 (monday..sunday)
 */
function weekday(date) { return (date.getUTCDay()+ 6) % 7 }

Answer 8

I think you can use moment-business-days.

Example:

// 22-11-2016 is Tuesday, DD-MM-YYYY is the format 
moment('22-11-2016', 'DD-MM-YYYY').businessAdd(5)._d // Tue Nov 29 2016 00:00:00 GMT-0600 (CST)