# 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:

```json
{
  "year": 2026
}
```

Response:

```json
{
  "result": {
    "weeks": 53
  }
}
```

## How to call it

### MCP

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

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

### HTTP (no key)

```sh
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](/v1/tools/iso-date-week-count-in-year/versions/1.0.0).

### CLI

```sh
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/](/clients/cli/).

## Related tools

- [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 is leap year](/tools/iso-date-is-leap-year): Test whether a proleptic Gregorian calendar year is a leap year.
- [ISO date range contains](/tools/iso-date-range-contains): Test whether an inclusive [start, end] date range contains a given date.
- [ISO date to week](/tools/iso-date-to-week): Convert a YYYY-MM-DD calendar date to an ISO-8601 week date.
- [ISO date age](/tools/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](/tools/iso-date-business-days-count): Count the business days in an inclusive date range, skipping caller-supplied weekend weekdays and holidays.