ISO date week count in year

iso-date-week-count-in-year · version 1.0.0 · Dates & times (UTC, ISO 8601) · free, no key needed

Return the number of ISO-8601 weeks (52 or 53) in an ISO week-numbering year.

Use when you need to: iso date week count in year · iso weeks in year · is 53 week year.

Supported

• iso date week count in year
• iso weeks in year
• is 53 week year

Not supported

• locale week numbers
• Sunday-first weeks
• fiscal weeks

Behavior

• year is a JSON integer 1-9999 and is interpreted as an ISO week-numbering year, which may span parts of two calendar years.
• An ISO week-numbering year has 53 weeks when 1 January falls on a Thursday, or when the year is a leap year and 1 January falls on a Wednesday. All other years have 52 weeks.

Input

• year (integer, required): min 1; max 9999

Output

• weeks (one of 52, 53, required)

Limits

• year min: 1
• year max: 9999

Example

Request input:

{
  "year": 2026
}

Response:

{
  "result": {
    "weeks": 53
  }
}

How to call it

MCP

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

{
  "id": "iso-date-week-count-in-year",
  "version": "1.0.0",
  "input": {
    "year": 2026
  }
}

HTTP (no key)

curl -X POST https://computefirst.net/v1/tools/iso-date-week-count-in-year/versions/1.0.0/execute \
  -H "Content-Type: application/json" \
  -d '{"year":2026}'

The machine-readable contract is at /v1/tools/iso-date-week-count-in-year/versions/1.0.0.

CLI

node cli.mjs run iso-date-week-count-in-year 1.0.0 --input input.json --base-url https://computefirst.net

Get the client at /clients/cli/.

Related 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 is leap year: Test whether a proleptic Gregorian calendar year is a leap year.
• ISO date range contains: Test whether an inclusive [start, end] date range contains a given date.
• ISO date to week: Convert a YYYY-MM-DD calendar date to an ISO-8601 week date.
• ISO date age: Compute the calendar-aware elapsed years, months, and days between a birth date and an as-of date.
• ISO date business days count: Count the business days in an inclusive date range, skipping caller-supplied weekend weekdays and holidays.