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ISO 8601:2019 · RFC 3339
Age Calculator
Precision chronology — exact to the day. Years, months, days, plus a live seconds-alive counter, Korean age and leap-year correction.
- Runs in your browser
- No data stored
- Free forever
As of:
0Years
0Months
0Days
0Weeks
0Hours
0Seconds
0seconds alive — live
Next birthday in00d 00h 00m 00s
Korean age–
Born on a–
Zodiac–
Method
How the age is computed
The tool measures the calendar interval between your date of birth and the reference date using ISO 8601:2019 rules — not a fixed 30-day month and not a 365-day year average. It counts whole years first, then whole months, then the leftover days, borrowing the real length of the previous month when needed.
- Full leap-year correction, including the century-year exception.
- February 29 birthdays resolve to Feb 28 in non-leap years.
- Six units at once: years, months, days, weeks, hours, seconds.
Place timeline.webp in /assets/img/
Understanding your result
The exact formula
Complete years equal the reference year minus the birth year, reduced by one when this year’s anniversary has not arrived yet. The month and day components are the remainder after the last full anniversary, computed against the genuine month lengths of the Gregorian calendar. This is identical to the spreadsheet expression =DATEDIF(dob, TODAY(), "Y") for years, with "YM" and "MD" for the leftover months and days.
Why month counts differ between tools
Some calculators divide total days by 30 or by 365.25, which drifts across February and long months. This theme uses the Gregorian calendar method: a complete month runs from one day-number to the same day-number of the next month, regardless of whether that month has 28, 30 or 31 days.
Working backwards
To recover a birth date from an age, subtract the age from the reference date. Someone who was 40 on 1 January 2026 was born on or before 1 January 1986. The reference-date field above lets you compute age as of any past or future day, not only today.
Methodology & sources
Built on published standards
Every figure on this page follows internationally recognised date-and-time standards, the same references used by clinical and actuarial software.
- ISO 8601:2019Date & time representation, intervals
- RFC 3339Internet date/time format
- Reingold & DershowitzCalendrical Calculations
What people are saying
45 reviews · 5 ★ averageSatyam Chaurasiya★★★★★
“Satyam Chaurasiya — exactly what I needed.”
Kundan Verma★★★★★
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Frequently Asked Questions
How accurate is this age calculator?
It uses ISO 8601:2019 interval arithmetic — the same standard applied in clinical software, government systems and actuarial calculations. Results are exact to the day with full leap-year correction, including the century-year exception rule.
What is the formula for calculating age from a date of birth?
Age in complete years = current year minus birth year, minus 1 if the birthday has not yet occurred this year. Months and days are the remainder, borrowing from the previous month using its real length (28, 29, 30 or 31 days) rather than an average. Spreadsheet users get the same answer with =DATEDIF(dob, TODAY(), "Y").
How does the calculator handle February 29 birthdays?
For people born on February 29, the calculator uses February 28 as the legal age-increment date in non-leap years and February 29 in leap years, following the international civil-registration standard. A person born Feb 29, 2000 turns 25 on Feb 28, 2025.
Why might my Korean age differ from my international age?
Traditional Korean age counts the gestation period as the first year, so newborns are age 1 at birth, and everyone gains a year on January 1. South Korea retired this for legal purposes in June 2023, but it remains culturally common.
What does the live seconds-alive counter show?
The exact number of seconds elapsed since your date of birth, updated every second in real time. A 30-year-old sees roughly 946 million seconds. It accounts for leap days and is computed from a Unix-timestamp baseline.
Can I find my age on a specific past or future date?
Yes. Change the reference-date field and the result recalculates against that date — useful for insurance age verification, legal thresholds and historical research.
Is this age calculator free and private?
Yes. It runs entirely in your browser and needs no sign-up. Your date of birth is never transmitted to a server or stored — the arithmetic happens on your own device.