Age Calculator

An exact age in years, months, and days, measured from a reference date — your local calendar date unless you supply a custom one.

How it works

• Parsed the birth date and reference date as calendar dates; when no reference is supplied, used the visitor's local calendar date (never UTC).
• Subtracted year, month, and day components and borrowed from the larger unit when needed.
• Also computed the totals: whole days and whole months.

• The totals in whole days and whole months are reported alongside the years/months/days breakdown.

Methodology

1. Parse the birth date and reference date as ISO 8601 calendar dates; when the reference is omitted, use the visitor's local calendar date rather than UTC.
2. Subtract year, month, and day components, borrowing from the next larger unit when a component is negative.
3. Also compute totals in whole days and whole months for comparison.

Time model

• Time source: the visitor's local date and clock.
• Timezone: The reference defaults to the visitor's local calendar date (browser local timezone). A supplied reference date is a plain calendar date and is not shifted by a timezone.
• Locale: Calendar dates are read and reported as ISO-8601 (YYYY-MM-DD); no locale-specific month or day ordering is applied.
• Daylight saving: Local calendar dates are compared as calendar days, so a daylight-saving change cannot shift the age by a day.
• Reference date: Optional. When omitted, the visitor's local calendar date is used; a supplied reference date overrides it. The reference is never silently taken from UTC.

Usage

1. Enter the birth date.
2. Optionally set a custom reference date (your local today by default).
3. Read the exact age and the totals in days and months.

Examples

These are examples, not current values: they use fixed inputs, while the interactive tool computes live results in your browser.

Exact age

{
  "birthDate": "1990-05-15",
  "reference": "2026-09-24"
}

Limitations

Why 'years, months, days' is not a duration

Months and years have variable length, so an exact age must be expressed as calendar components. The totals (days and months) give a single number for comparisons, while the components give the colloquial answer.