Time calculator

Age Calculator

Q: How does this age calculator work?

It subtracts the birth date from the reference date using Gregorian calendar arithmetic: complete years first, then remaining months, then remaining days (borrowing from the previous month when the day count goes negative). It also reports the total number of calendar days between the two dates.

Q: What is chronological age?

Chronological age is the exact elapsed time since birth (or another start date), measured on the calendar. It is the standard used for legal eligibility, school cutoffs, medical dosing by age, and official documents — as opposed to biological or developmental age.

Q: Can I find my age on a past or future date?

Yes. Set Birth date to the date of birth and Age on date to any target day — past or future — to get the exact age as of that day.

Q: How are leap years and February 29 handled?

Month lengths follow the Gregorian leap-year rule (divisible by 4, with the century/400 exception). When borrowing days into a shorter previous month, February contributes 28 or 29 days as appropriate. For people born on February 29, many civil systems treat February 28 as the anniversary in non-leap years.

Q: Why do some calculators disagree on months and days?

Uneven month lengths create ambiguous edge cases, especially at month ends (e.g. Feb 28 to Mar 31). This calculator uses the common “same calendar day” method: treat Feb 28 → Mar 28 as one month, then add the leftover days. Tools that use fixed 30-day months or end-of-month alignment can differ by a few days.

Q: How is age counted in other cultures?

Most Western legal systems start at age 0 and add one year on each birthday. Traditional East Asian reckoning may start at 1 at birth and increment at Lunar New Year. Traditional Korean age (Sae-neun-nai) also started at 1 and incremented every January 1; South Korea retired that system for official use in 2023, though it remains culturally familiar. This calculator reports Western chronological age.

Q: Can I use this for monuments, products, or other objects?

Yes. Put the construction, manufacture, or acquisition date in Birth date and the date you care about in Age on date. The same calendar interval applies.

Q: Is this result official for legal or medical filings?

The arithmetic matches common civil calendar practice and is suitable for everyday planning. For retirement, insurance, immigration, or clinical decisions, confirm against the authority’s rules and your own records.

Calculate exact age in years, months, and days from a birth date to today or a chosen date. Runs locally in your browser. Free online tool — no sign-up.

Instant result

Result

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Enter values to calculate.

Inputs—

Mode—

Formula—

Trust summary Engine tested · Specification checked · v1.0.1

Input interpretation: Enter values to calculate.
Result: —
Model: Chronological age between a birth (start) date and a reference date in years, months, and days, plus total days elapsed.
Scope: Gregorian calendar dates in the local date fields (no time-of-day).
Verification: Engine tested · Specification checked · v1.0.1
Named expert review: Optional · Not performed
Specification basis: Gregorian calendar month lengths and leap-year rule
Western chronological age (birthday anniversary)
Common civil practice for February 29 anniversaries in non-leap years
Specification basis

Formulas

Core equations used by this calculator.

YearsY = year(on) − year(birth), then adjust if birthday not yet reached

Months & daysBorrow days from prior month, then months from years as needed

Total daysDays = floor((on − birth) / 86,400,000 ms)

iThis tool uses calendar age (complete years, then remaining months and days), not a fixed 30-day month. End-of-month pairs (e.g. Feb 28 → Mar 31) follow the “same day number” borrow method used by most Western age calculators.

How to use

Enter the birth date

Choose the person’s (or object’s) date of birth / start date.

Choose the reference date

Leave as today for current age, or pick any past or future date to find age on that day.

Read years, months, and days

The result shows calendar age plus the total number of days between the two dates.

Example calculations

Common configurations with formula and result.

Current age

Born May 15, 1990; age on Apr 14, 2026

2026−1990, birthday not yet passed → −1 year

35y 10m 30d

Birthday already passed

Born Mar 14, 1979; age on Apr 15, 2026

Years stay 47; months 1; days 1

47y 1m 1d

Long subtraction

Born Nov 15, 2006; age on Mar 10, 2026

Borrow days & months as needed

19y 3m 23d

End of month

Feb 28, 2022 → Mar 31, 2022

Feb 28→Mar 28 = 1 month, then +3 days

0y 1m 3d

Days in each month

Common values at a glance.

Month	Days (common year)	Days (leap year)
January	31	31
February	28	29
March	31	31
April	30	30
May	31	31
June	30	30
July	31	31
August	31	31
September	30	30
October	31	31
November	30	30
December	31	31

i A Gregorian leap year is divisible by 4, except century years must also be divisible by 400 (2000 was a leap year; 2100 is not).

Age calculator specification

Version 1.0.1 · Engine tested

Calculation status

Engine tested 4 published cases
Named expert review Not performed
Calculation version 1.0.1

Review policy

Definition: Chronological age is the elapsed calendar interval between a date of birth (or start date) and a reference date, usually expressed in completed years, months, and days on the Gregorian calendar. Age increases on the birthday anniversary in the Western system used by most legal and medical contexts.
What it calculates: Chronological age between a birth (start) date and a reference date in years, months, and days, plus total days elapsed.
Inputs: Birth date (date of birth or start date)
Age on date (reference date; defaults to today)
Outputs: Age as Y years, M months, D days
Total calendar days between the two dates
Formula: Calendar borrow method for Y/M/D; total days = floor((on − birth) / 86400000 ms)
Assumptions: Gregorian calendar dates in the local date fields (no time-of-day).
Western age system: age starts at 0 and increases on the birthday anniversary.
Reference date must be on or after the birth date.
Calculation runs locally in the browser.
Units: Years, months, days (calendar)
Total days (elapsed calendar days)
Boundary conditions: Invalid dates or on < birth → no age result
Month-end pairs may differ from tools that align both ends of month
Example: Born 2006-11-15, on 2026-03-10 → 19y 3m 23d
Validation cases: 4 published on this page
1979-03-14 → 2026-04-15 → 47y 1m 1d
2006-11-15 → 2026-03-10 → 19y 3m 23d
2022-02-28 → 2022-03-31 → 0y 1m 3d
1990-05-15 → 2026-04-14 → 35y 10m 30d
Specification basis: Gregorian calendar month lengths and leap-year rule
Western chronological age (birthday anniversary)
Common civil practice for February 29 anniversaries in non-leap years
Calculation version: 1.0.1

Background

Interpretation and common distinctions.

What is an age calculator?

An age calculator finds the chronological interval between two calendar dates — typically a date of birth and today, or any other reference day. Results are shown in years, months, and days, plus the total number of days lived (or elapsed). The same tool works for people, pets, products, buildings, and historical events: enter the start date and the date you want age “as of.”

This page uses the Western (Gregorian) age system: age starts at zero at birth and increases by one year on each birthday. That is the system used for most legal, school, and medical purposes worldwide. Other cultural systems count differently (see FAQ).

How to calculate age by hand

Treat the dates as year / month / day subtraction, borrowing when needed:

Subtract days. If the result is negative, borrow one month: add the number of days in the previous month of the later date, then reduce months by 1.
Subtract months. If negative, borrow 1 year (add 12 months) and reduce years by 1.
Subtract years.

Worked example

Age on 10 March 2026 for someone born 15 November 2006:

Days: 10 − 15 needs a borrow. February 2026 has 28 days → 10 + 28 − 15 = 23 days; months become 3 − 1 = 2.
Months: 2 − 11 needs a borrow → 2 + 12 − 11 = 3 months; years become 2026 − 1 = 2025.
Years: 2025 − 2006 = 19.

Result: 19 years, 3 months, 23 days.

Another check: born 14 March 1979, age on 15 April 2026 → 47 years, 1 month, 1 day.

Leap years and February 29

A year is a leap year if divisible by 4, except century years must also be divisible by 400.
February has 28 days in a common year and 29 in a leap year; borrowing into February uses that length.
People born on 29 February typically celebrate (and legally age) on 28 February in non-leap years in many jurisdictions — then on the 29th again in leap years.

Month-end edge cases

Because months have different lengths, end-of-month spans can be interpreted two ways. Example: 28 Feb 2022 → 31 Mar 2022.

Same-day method (this calculator): Feb 28 → Mar 28 is one month, then 3 leftover days → 1 month 3 days.
End-of-month alignment: treat both dates as month ends → 1 month only.

Both are reasonable; we follow the former, matching common Western civil calendar practice.

When exact age matters

Exact age (to the day) shows up in:

School enrollment cutoffs (often a fixed calendar date each year)
Medical and paediatric contexts that track age in days or months
Retirement and benefits windows tied to exact ages (e.g. full retirement age in years and months)
Insurance and legal documents with age thresholds
Genealogy lifespan checks from historical records

For interval questions that are not “how old,” related time tools on this site cover day, week, month, and second counts in a year.

Other calculators in this family: Days in a Year, Months of the Year, Weeks in a Year, Seconds in a Day, UTC Time .

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Frequently asked questions

Key distinctions behind the calculation.

How does this age calculator work?