Current Age
{{ ageReadable }}
{{ yearsTotal }} yrs {{ monthsTotal }} mos {{ daysTotal }} days
Next BD: {{ nextBirthdayStr }} {{ daysToBirthday }} days left
Years {{ yearsTotal }}
Months {{ monthsTotal }}
Weeks {{ weeksTotal }}
Days {{ daysTotal }}
{{ row.label }} {{ row.value }}
  • Day of week born:{{ birthWeekday }}
  • Western zodiac:{{ zodiacWestern }}
  • Chinese zodiac:{{ zodiacChinese }}
  • Year progress: {{ passedPct }} % / {{ passedDays }} d
{{ passedPct }} % | {{ passedDays }} d
{{ passedPct }} % / {{ passedDays }} d elapsed • {{ remainPct }} % / {{ remainDays }} d remaining
Categories: Date & Time
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Age expresses the exact interval between a person’s birth date and a chosen reference date, traditionally reported in years yet grounded in smaller calendar units. Understanding it supports legal compliance, milestone planning, and demographic insight.

This calculator lets you enter any date of birth and an optional age at date. A reactive engine transforms those inputs into a complete breakdown—years to seconds—plus Western and Chinese zodiac signs, days until the next birthday, and the current year’s progress.

Event planners, teachers, and HR staff can, for example, confirm that someone born 1 January 1990 turns 35 on 1 January 2025 and has 201 days left. Always cross-check official records when legal precision is required.

Technical Details:

Concept Overview

Calendar age calculation counts whole Gregorian years first, then resolves remaining months and days to eliminate variable-length months. Supplementary totals (weeks, hours, minutes, seconds) derive from absolute day differences. Zodiac logic maps birth dates to fixed Western cut-off points and a 12-year Chinese cycle.

Core Equation

The fundamental relation is:

Age= Y,M,D Y=⌊ t−b 1 year ⌋

Here t is the target date, b the birth date, and the remainder is re-decomposed into months and days. Subsequent divisions convert total seconds into larger units.

Zodiac Cut-offs

SignStart DateEnd Date
Capricorn22 Dec19 Jan
Aquarius20 Jan18 Feb
Pisces19 Feb20 Mar
Aries21 Mar19 Apr
Taurus20 Apr20 May
Gemini21 May20 Jun
Cancer21 Jun22 Jul
Leo23 Jul22 Aug
Virgo23 Aug22 Sep
Libra23 Sep22 Oct
Scorpio23 Oct21 Nov
Sagittarius22 Nov21 Dec

The sign names give cultural context only; they do not influence numerical outputs.

Variables & Parameters

  • date of birth – ISO-8601 date, starting point for age.
  • age at date – optional ISO-8601 date; defaults to today.
  • calendar system – proleptic Gregorian.
  • year length – actual, not average, ensuring leap-year accuracy.

Worked Example

Birth date = 2000-02-29; Target date = 2025-06-14 → Age = 25 y 3 m 16 d; Totals = 303 months, 1320 weeks, 9241 days, 221 784 hours.

Assumptions & Limitations

  • Operates solely on the Gregorian calendar.
  • Ignores time-zones; all dates are local browser dates.
  • Excludes time-of-day; precision is calendar-day.
  • No support for calendar reforms before 1582.

Edge Cases & Error Sources

  • Birth date after target date yields negative values.
  • February 29 birthdays on non-leap years shift to March 1 in legal contexts.
  • Browser locale mismatches may misinterpret numeric month/day order.
  • Extreme historical dates (< 1900) can exceed integer limits in some environments.

Scientific Validity & References

Methodology aligns with ISO-8601 calendrical calculations and common demographic practice. See Rata Die (Neugebauer, 1979) and Gregorian reform analyses for canonical formulas.

Privacy & Compliance

No sensitive data is transmitted; all computations remain inside your browser, aligning with GDPR local-processing guidance.

Step-by-Step Guide:

Follow these steps to obtain a full age profile.

  1. Select a date of birth.
  2. (Optional) Pick an age at date; leave blank for today.
  3. Inspect the summary badges for quick years-months-days and time-to-birthday.
  4. Switch tabs to view unit totals, breakdown table, or extra zodiac and year-progress insights.
  5. Update either date anytime to recalculate instantly.

FAQ:

Is my data stored?

No. All inputs stay in the browser session and disappear when the page closes.

How are leap years handled?

The calculator uses actual Gregorian rules—years divisible by 4 except centuries not divisible by 400.

Why do month totals vary?

Months reflect calendar lengths; February contributes 28 or 29 days, while July contributes 31.

Can I include time-of-day?

Current version rounds to whole days; time-of-day adds negligible accuracy for age legislation.

What calendars are supported?

Only the proleptic Gregorian calendar is used, matching modern civil standards worldwide.

Glossary:

Gregorian Year
365 days, with a leap day every four years except centuries not divisible by 400.
Zodiac Sign
Astrological label assigned by date-range; cultural, not scientific.
Chinese Cycle
Twelve-year animal cycle starting with the Rat.
Proleptic
Extends a calendar backward before its historic adoption.
Unix Timestamp
Seconds since 1 January 1970 UTC, basis for total-seconds output.

No data is transmitted or stored server-side.