ISO date age

iso-date-age · version 1.0.0 · Dates & times (UTC, ISO 8601) · free, no key needed

Compute the calendar-aware elapsed years, months, and days between a birth date and an as-of date.

Use when you need to: iso date age · age in years months days · elapsed calendar time between dates.

Supported

• iso date age
• age in years months days
• elapsed calendar time between dates

Not supported

• negative age
• total days or months as a single unit (use iso-date-difference or iso-date-add-months)
• timezones

Behavior

• birth_date and as_of_date are strict YYYY-MM-DD proleptic Gregorian UTC calendar dates with year 0001-9999. birth_date must not be after as_of_date.
• total_months is the largest whole-month count m such that birth_date plus m whole months (day clamped to the target month, as in iso-date-add-months) does not exceed as_of_date.
• years = floor(total_months / 12), months = total_months mod 12.
• days is the remaining whole days from (birth_date plus total_months months, clamped) to as_of_date, computed on the civil day serial so it is never negative and never depends on a fixed 28/29/30/31 assumption.
• For a birth date of 29 February, the year is not counted as complete until 1 March in non-leap as_of years (29 February clamps to 28 February when added, so day 1 of March is needed to complete the year).

Input

• birth_date (string, required): min length 10; max length 10; pattern ^\d{4}-\d{2}-\d{2}$
• as_of_date (string, required): min length 10; max length 10; pattern ^\d{4}-\d{2}-\d{2}$

Output

• years (integer, required): min 0
• months (integer, required): min 0; max 11
• days (integer, required): min 0; max 30

Limits

• year min: 1
• year max: 9999

Example

Request input:

{
  "birth_date": "2020-01-15",
  "as_of_date": "2026-09-15"
}

Response:

{
  "result": {
    "years": 6,
    "months": 8,
    "days": 0
  }
}

How to call it

MCP

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

{
  "id": "iso-date-age",
  "version": "1.0.0",
  "input": {
    "birth_date": "2020-01-15",
    "as_of_date": "2026-09-15"
  }
}

HTTP (no key)

curl -X POST https://computefirst.net/v1/tools/iso-date-age/versions/1.0.0/execute \
  -H "Content-Type: application/json" \
  -d '{"birth_date":"2020-01-15","as_of_date":"2026-09-15"}'

The machine-readable contract is at /v1/tools/iso-date-age/versions/1.0.0.

CLI

node cli.mjs run iso-date-age 1.0.0 --input input.json --base-url https://computefirst.net

Get the client at /clients/cli/.

Related tools

• ISO date business days count: Count the business days in an inclusive date range, skipping caller-supplied weekend weekdays and holidays.
• ISO date days in month: Return the number of calendar days in a given proleptic Gregorian year and month.
• ISO date difference: Whole days from start to end as a canonical integer string (end - start).
• ISO date range list: Enumerate the dates in an inclusive [start, end] range stepped by a whole number of days.
• ISO date weekday occurrences in range: List every date within an inclusive date range that falls on a given ISO weekday.
• ISO date add months: Add a signed month count to a YYYY-MM-DD date, clamping the day to the target month.