What This Calculator Does
This age calculator determines your precise age in years, months, and days based on your date of birth and a target date. It also shows the total number of days you have lived and counts down the days until your next birthday. The calculation accounts for varying month lengths and leap years.
Inputs Explained
- Date of Birth: Your birth date in YYYY-MM-DD format. This is the starting point for the age calculation.
- Age at the Date of: The target date to calculate your age at. Defaults to today's date but can be set to any past or future date.
- Time Zone: The IANA time zone used for date interpretation. Defaults to your local browser time zone.
How It Works
The calculator uses the Luxon date-time library to perform calendar-aware arithmetic. It first counts the number of complete years between the two dates, then the remaining complete months, and finally the leftover days. This gives the standard "X years, Y months, Z days" format. The total days lived is calculated separately as a simple day count between the two dates. For the birthday countdown, the calculator checks whether your birthday has already passed this year; if so, it targets next year's date.
Formula Used
Age = Target Date − Date of Birth
Expressed as: Y years, M months, D days
Total Days = floor(Target Date − Date of Birth) in calendar days
Next Birthday = DOB set to current/next year (whichever is upcoming)
Expressed as: Y years, M months, D days
Total Days = floor(Target Date − Date of Birth) in calendar days
Next Birthday = DOB set to current/next year (whichever is upcoming)
Age Calculator
Calculate your exact age in years, months, and days.
Your Age
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Years, Months, Days
Time Zone
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Date (Formatted)
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Timestamp (ms)
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Total Days Lived
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Next Birthday
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Days Until Birthday
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Step-by-Step Example
Date of Birth: January 1, 2000
Target Date: January 31, 2026
Step 1: Count complete years from Jan 1, 2000 to Jan 1, 2026 = 26 years.
Step 2: Count remaining months from Jan 1 to Jan 31 = 0 complete months.
Step 3: Count remaining days from Jan 1 to Jan 31 = 30 days.
Result: 26 years, 0 months, 30 days. Total days lived: 9,527.
Next Birthday: January 1, 2027 — 335 days away.
Use Cases
- Legal age verification: Confirm whether someone meets a minimum age requirement for contracts, voting, or driving.
- Retirement planning: Calculate the exact number of years and days until a target retirement age.
- Healthcare: Determine a patient's precise age for medical records, vaccination schedules, or insurance eligibility.
- Education: Check whether a child meets the age cutoff for school enrollment or grade placement.
- Personal curiosity: Find out exactly how old you are in days, or count down to your next birthday.
Assumptions and Limitations
- The calculator uses the Gregorian calendar exclusively. Dates in other calendar systems are not supported.
- Leap years (including century exceptions where divisible by 400) are handled correctly by the Luxon library.
- The "Age at the Date of" field defaults to today but can be set to any date, including future dates.
- Time zone selection affects how the date boundaries are interpreted but not the day count itself.
- Results are deterministic — the same inputs always produce the same output.
Disclaimer: This calculator provides estimates for informational purposes. For legal age verification or medical purposes, consult appropriate professionals or official records.
Frequently Asked Questions
The calculator counts the number of full years between your date of birth and the target date first. It then counts the remaining full months after subtracting those years, and finally the leftover days. This gives you the standard representation used in most legal and everyday contexts. Varying month lengths (28, 29, 30, or 31 days) are accounted for automatically by the underlying calendar library.
Yes. The calculator uses the Luxon date-time library, which correctly identifies leap years — years divisible by 4, except for century years not divisible by 400. February 29 is properly included in calculations involving leap year dates. If your birthday is February 29, the next birthday calculation will correctly target the next leap year occurrence.
Absolutely. Set the 'Age at the Date of' field to any future date to see what your age will be at that point. This is useful for retirement planning, milestone birthdays, or checking eligibility for age-restricted activities at a specific future date.
The time zone determines how date boundaries are interpreted. For most users, the default (your browser's local time zone) is correct. If you were born in a different time zone from where you currently live and the exact date boundary matters, select the time zone of your birth location for the most accurate result.
Total days lived is the simple count of calendar days between your date of birth and the target date. This is a straight subtraction of the two dates converted to day units. Leap days are included whenever February 29 falls within the range. The count does not include the birth date itself — day one of life is the day after birth.
No. All calculations happen entirely in your browser using JavaScript. No dates are sent to any server, and nothing is stored. Your privacy is fully preserved. You can verify this by using the calculator while disconnected from the internet.
Chronological age is the straightforward count of time since birth, which is what this calculator computes. Biological age refers to how old your body appears to be based on health markers like telomere length, organ function, and fitness levels. The two can differ significantly depending on lifestyle and genetics.
Yes. You can enter any valid Gregorian calendar date as the date of birth. However, the Gregorian calendar was adopted at different times across different countries, so for dates before the 18th century in some regions, the results may not align with historical local calendars that were in use at the time.
Sources and References
- IANA Time Zone Database — Official source for global time zone data used by the Luxon library in this calculator.
- Luxon Documentation (Moment.js successor) — The date-time library powering the calendar-aware arithmetic behind the age calculation.
- Gregorian Calendar – Encyclopaedia Britannica — Reference for the Gregorian calendar system and leap year rules used in this calculator.
- ISO 8601 Date and Time Format — International standard for date and time representation used for input parsing.
- Schema.org FAQPage Specification — Structured data standard used to mark up the FAQ section on this page.