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:

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

Response:

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

How to call it

MCP

Connect https://computefirst.net/mcp (setup), then call execute with:

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

HTTP (no key)

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.

CLI

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/.

Related 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: List every date within an inclusive date range that falls on a given ISO weekday.
• 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: Return the number of calendar days in a given proleptic Gregorian year and month.
• 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: Return the last valid calendar day of the year-month of a YYYY-MM-DD date.