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Free Age Calculator

Calculate your exact age in years, months, days, hours, and total days. Find your zodiac sign and days until your next birthday.

Works offline once loaded

Common uses

  • Calculate Exact Age for BirthdaysFind the exact age in years, months, and days β€” perfect for milestone birthdays and age verification.
  • Verify Age for Legal RequirementsCalculate exact age for legal age verification β€” alcohol, voting, driving, retirement, and more.
  • Find Your Zodiac and Chinese Zodiac SignDiscover your Western zodiac sign and Chinese zodiac animal from your birth date.
  • Calculate Historical AgesFind out how old historical figures, celebrities, or relatives were at any specific historical date.
  • Track Age MilestonesCalculate when you will reach age milestones β€” 10,000 days, 1 billion seconds, retirement age, and more.

How It Works

The age calculator is a zero-dependency tool with no external libraries. All arithmetic runs directly in the browser using JavaScript's built-in Date object and integer math, with no library, no server call, and no data ever leaving your device.

  1. 1
    Local date parsing
    When you enter a birth date, the tool parses the YYYY-MM-DD string into numeric year, month, and day parts and constructs a Date using the three-argument constructor. This deliberately sidesteps a subtle browser bug: the standard new Date('2001-06-01') parses as UTC midnight, which shifts the weekday and calendar date backward by one day for anyone in a negative-UTC-offset timezone.
  2. 2
    Gregorian calendar arithmetic
    The calcAge function subtracts birth from the reference date field by field β€” years, then months, then days β€” borrowing from the next unit when the result goes negative (the same carry-borrow logic a paper calendar uses). It also derives totals in days, weeks, months, and hours directly from the millisecond difference between the two timestamps.
  3. 3
    Zodiac and milestone computation
    Western zodiac is determined by a hardcoded date-range table; Chinese zodiac maps birth year to one of 12 animals via modular arithmetic on the year, with a note if you were born in January or early February when the Chinese New Year boundary is ambiguous. Upcoming milestones (next round-decade birthday, next 5,000-day mark, next billionth second of life, half-birthday) are computed by adding fixed offsets to the birth date using calendar-safe date addition that avoids daylight-saving-time drift.
  4. 4
    Formatted output and shareable link
    Results are formatted with the browser's built-in Intl.DateTimeFormat (via toLocaleDateString) so dates render in your locale's preferred style. The 'copy link' button encodes the birth date and reference date in the link's #fragment using the browser's URLSearchParams API β€” the fragment is never sent to any server β€” letting you share or bookmark a specific calculation.

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Frequently Asked Questions