# Add business days

Industry: Core

`addBusinessDays` moves a date forward by working days. With no calendar it counts Monday to Friday.

```js
import { addBusinessDays } from "@northguild/gmt/plain/calculate";

addBusinessDays("2024-03-15", 1); // "2024-03-18"
```

2024-03-15 is a Friday, so the next working day is Monday 2024-03-18.

## A weekend that is not Saturday and Sunday

Pass the weekend as ISO weekday numbers (Monday is 1, Sunday is 7), the holidays as dates, and the time zone. Saudi Arabia in `Asia/Riyadh` has its weekend on Friday and Saturday, so `[5, 6]`.

```js
import { addBusinessDays } from "@northguild/gmt/plain/calculate";

addBusinessDays("2024-07-04", 1, {
  weekend: [5, 6],
  holidays: [],
  timeZone: "Asia/Riyadh",
}); // "2024-07-07"
```

2024-07-04 is a Thursday. Friday 07-05 and Saturday 07-06 are weekend days, so the answer is Sunday 2024-07-07.

Temporal's `PlainDate` has no working-day operation, so this is a function you call on the string, not a method on a value. The result is a date string again.

## Holidays come from you

GMT holds no holiday list. You pass the dates your organisation treats as non-working, in the format `YYYY-MM-DD`.

```js
import { nextBusinessDay } from "@northguild/gmt/calendar/business";

nextBusinessDay("2024-03-15", {
  weekend: [6, 7],
  holidays: ["2024-03-18"],
  timeZone: "Africa/Nairobi",
}); // "2024-03-19"
```

Monday 2024-03-18 is in the list, so the next working day after Friday is Tuesday 2024-03-19.

## Count working days between two dates

```js
import { businessDaysBetween } from "@northguild/gmt/calendar/business";

businessDaysBetween("2024-03-15", "2024-03-22", {
  weekend: [6, 7],
  holidays: [],
  timeZone: "Europe/Berlin",
}); // 5
```

## What to expect

| Call | Input | Result |
| --- | --- | --- |
| `addBusinessDays(value, 1)` | Friday 2024-03-15 | `"2024-03-18"` |
| `addBusinessDays(value, 1, calendar)` | Thursday 2024-07-04, weekend `[5, 6]` | `"2024-07-07"` |
| `nextBusinessDay(value, calendar)` | Friday 2024-03-15, holiday 2024-03-18 | `"2024-03-19"` |
| `businessDaysBetween(start, end, calendar)` | 2024-03-15 to 2024-03-22 | `5` |
| `addBusinessDays(value, 0)` | Saturday 2024-03-16 | `"2024-03-16"` |

An `amount` of 0 returns the input unchanged, even when it falls on a non-working day. Use `rollDate` to move a non-working day onto a working one.

Checked on 2026-10-26 with GMT 1.20.0.

See also: [`addBusinessDays`](/gmt/reference/plain/calculate/addBusinessDays/), [`nextBusinessDay`](/gmt/reference/calendar/business/nextBusinessDay/), [`businessDaysBetween`](/gmt/reference/calendar/business/businessDaysBetween/), [`rollDate`](/gmt/reference/calendar/business/rollDate/). [Migrate from date-fns](/gmt/migrate/date-fns/) lists the fixed-weekend `addBusinessDays` there.