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CrateX.app

Age Calculator

Calculate exact age in years, months, days, and total days from a birth date and an as-of date.

Use the calendar date, not a time of day.
Change this to calculate age on a past or future date.

Result

Exact age

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Total days

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Age Calculator

Quick Start

1
Enter the birth date, then choose the date you want to calculate age against.
2
Read the exact years-months-days age separately from total days; they answer different questions.
3
For enrollment dates, birthdays, or deadlines, change only the as-of date.

Common Scenarios

Birthdays and anniversaries

check how many full years, months, and days have passed.

Age on a selected date

see age on a past or future calendar date.

Total days

useful for records, planning, or rough day-count checks.

Calculation Method & Date Rules

Calendar age: the calculator counts full years first, then full months, then the remaining days from the birth date to the as-of date.
Real calendar months: month lengths and leap years come from the selected dates; the calculator does not average every month to 30 or 31 days.
Total days: reports the exclusive day gap between the two dates, so the birth date is not counted as day one.
As-of date: change it to answer how old someone was or will be on a birthday, enrollment date, deadline, or future date.
Chronological age only: it does not calculate lunar age, Korean age, biological age, legal eligibility, or timezone-based birth times.

Usage Advice

Dates are treated as calendar days, not timezone timestamps.
Total days uses the gap between dates; add 1 day if your rule counts the start day.
If your browser does not show a date picker, enter dates as YYYY-MM-DD.

URL Quick Fill

Prefill the age calculator from the URL hash. birth-date is required; as-of-date is optional and defaults to today.
birth-date: Birth date (required)
as-of-date: As-of date (optional, defaults to today)
Example: #birth-date=2000-05-10&as-of-date=2026-04-29
Hash parameters stay in the browser for tool prefill; CrateX.app does not record them.
Do not put private birth dates, client names, or other sensitive details in URLs.

Limitations & Compatibility

This tool does not interpret birth time, birthplace, timezones, or astrology-style rules.
Schools, exams, insurance, or legal age cutoffs can have their own inclusion rules.
Leap-day birthdays are calculated by calendar math; verify separately if an organization treats Feb 29 as Feb 28 or Mar 1.

Privacy & Security

Calculations run in your browser. Current values stay in the current browser session by default.

FAQ

6

Continue with these related tools for the next step.

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All tool processing happens locally in your browser.