Age Calculator — Chronological Age from Birthdate
Calculate calendar age from a birth date and an as-of date (UTC YYYY-MM-DD). Sample: born 2000-01-01 as of 2026-08-09 → 26 years, 7 months, 8 days. Browser-only.
How it works
Pick a birth date and an as-of date. Age is the calendar difference (years, then leftover months and days), plus total whole days between the dates.
Formula
Parse YYYY-MM-DD as UTC midnight. Subtract calendar components with month/day borrow; totalDays = (asof−birth)/86400000. Notes:
- Uses calendar months, not a fixed 30-day month.
- Ignores local timezone offsets by using UTC date parts.
- Leap days affect day totals when they fall in the interval.
Example
Example: birth 2000-01-01, as-of 2026-08-09 → 26 years, 7 months, 8 days.
When to use it
- Forms that need age in Y/M/D.
- Homework on calendar differences.
- Pair with date-difference for span drills.
Frequently asked questions
Sample?
2000-01-01 to 2026-08-09 → 26y 7m 8d.
Timezone?
Dates are treated as UTC calendar days.
Future birth?
As-of must be ≥ birth.
Advice?
Educational only.
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Questions or feedback
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