# ISO date nth weekday of month

`iso-date-nth-weekday-of-month` · version 1.0.0 · Dates & times (UTC, ISO 8601) · free, no key needed

Return the date of the nth occurrence of an ISO weekday within a calendar month.

**Use when you need to: iso date nth weekday of month · third monday of month · nth weekday in month.**

## Supported

- iso date nth weekday of month
- third monday of month
- nth weekday in month

## Not supported

- negative indexing (use iso-date-last-weekday-of-month)
- timezones
- locale weekday names

## Behavior

- year is a JSON integer 1-9999, month is a JSON integer 1-12.
- weekday is a JSON integer 1-7 with Monday=1 .. Sunday=7. n is a JSON integer 1-5.
- Returns the date of the nth time that weekday occurs in that calendar month, counting from the first day of the month.
- Rejected if the month does not have an nth occurrence of that weekday (for example a 5th Monday in a short month).

## Input

- `year` (integer, required): min 1; max 9999
- `month` (integer, required): min 1; max 12
- `weekday` (integer, required): min 1; max 7
- `n` (integer, required): min 1; max 5

## Output

- `date` (string, required): min length 10; max length 10

## Limits

- year min: 1
- year max: 9999
- n min: 1
- n max: 5

## Example

Request input:

```json
{
  "year": 2026,
  "month": 9,
  "weekday": 1,
  "n": 3
}
```

Response:

```json
{
  "result": {
    "date": "2026-09-21"
  }
}
```

## How to call it

### MCP

Connect `https://computefirst.net/mcp` ([setup](/docs#connect)), then call `execute` with:

```json
{
  "id": "iso-date-nth-weekday-of-month",
  "version": "1.0.0",
  "input": {
    "year": 2026,
    "month": 9,
    "weekday": 1,
    "n": 3
  }
}
```

### HTTP (no key)

```sh
curl -X POST https://computefirst.net/v1/tools/iso-date-nth-weekday-of-month/versions/1.0.0/execute \
  -H "Content-Type: application/json" \
  -d '{"year":2026,"month":9,"weekday":1,"n":3}'
```

The machine-readable contract is at [/v1/tools/iso-date-nth-weekday-of-month/versions/1.0.0](/v1/tools/iso-date-nth-weekday-of-month/versions/1.0.0).

### CLI

```sh
node cli.mjs run iso-date-nth-weekday-of-month 1.0.0 --input input.json --base-url https://computefirst.net
```

Get the client at [/clients/cli/](/clients/cli/).

## Related tools

- [ISO date last weekday of month](/tools/iso-date-last-weekday-of-month): Return the date of the last occurrence of an ISO weekday within a calendar month.
- [ISO date weekday occurrences in range](/tools/iso-date-weekday-occurrences-in-range): List every date within an inclusive date range that falls on a given ISO weekday.
- [ISO date day of year](/tools/iso-date-day-of-year): Return the ordinal day number (1-366) of a YYYY-MM-DD date within its calendar year.
- [ISO date days in month](/tools/iso-date-days-in-month): Return the number of calendar days in a given proleptic Gregorian year and month.
- [ISO date from day of year](/tools/iso-date-from-day-of-year): Convert a calendar year and ordinal day number (1-366) to a YYYY-MM-DD date.
- [ISO date month end](/tools/iso-date-month-end): Return the last valid calendar day of the year-month of a YYYY-MM-DD date.