Is age inclusive or exclusive?

Exclusive — you 'turn' a new year on the morning of your birthday. The calculator considers someone born on May 13 to be one year old on May 13 the following year, not May 14.

Does it handle leap years correctly?

Yes. People born on February 29 are treated as turning a year older on March 1 in non-leap years, which is the legal convention in most jurisdictions.

Why does the day count borrow from the previous month?

Because months aren't all the same length. To express 'four months and 30 days' as a single answer, the calculator borrows the previous month's day count, exactly like long subtraction.

What time of day does it assume?

Midnight local time on both dates. Birth time of day isn't considered — none of the standard age-counting conventions use it.

Can I compute someone else's age?

Yes — the calculator doesn't know whose date of birth you entered. Use it for kids, pets (if their lifespan fits in the year range), or yourself.

Is my date sent anywhere?

No. The calculator runs entirely in your browser.

Age Calculator

Date of birth in — years, months, days (and total days alive) out.

The age calculator returns your exact age as years + months + days rather than a single decimal number. It also surfaces three running totals — total days, weeks, and months alive — that come up often in milestones, retrospectives, and personal goal-setting. Every calculation respects real month lengths and leap years, so the result agrees with what a clinician or a court would write. Date input follows ISO 8601; for computing arbitrary-instant differences see the Unix timestamp converter. For the calendar arithmetic behind the calculation — leap-year rules, month-length handling, and how cultures count age differently — see our age-calculation methodology.

Date of birth

As of

Your age

years, 1 month, 13 days

Total days: 13,193
Total weeks: 1,884
Total months: 433

How to use

Set your date of birth
Use the date picker; the calculator handles any year from the 1900s onwards (and works for future dates too, if you flip the second field).
Choose the 'as of' date
Defaults to today — change it to compute age at a milestone (a school start date, a retirement date, the day a contract begins).
Read the breakdown
Years/months/days is the canonical form most institutions accept. Total days is helpful for habit-formation reflections; total months for parents tracking growth in early life.

Frequently asked questions

Is age inclusive or exclusive?: Exclusive — you 'turn' a new year on the morning of your birthday. The calculator considers someone born on May 13 to be one year old on May 13 the following year, not May 14.
Does it handle leap years correctly?: Yes. People born on February 29 are treated as turning a year older on March 1 in non-leap years, which is the legal convention in most jurisdictions.
Why does the day count borrow from the previous month?: Because months aren't all the same length. To express 'four months and 30 days' as a single answer, the calculator borrows the previous month's day count, exactly like long subtraction.
What time of day does it assume?: Midnight local time on both dates. Birth time of day isn't considered — none of the standard age-counting conventions use it.
Can I compute someone else's age?: Yes — the calculator doesn't know whose date of birth you entered. Use it for kids, pets (if their lifespan fits in the year range), or yourself.
Is my date sent anywhere?: No. The calculator runs entirely in your browser.

About

How age counting differs by culture

Most of the world counts age in completed solar years from the day of birth. Until 2023, Korea used a system where everyone was age 1 at birth and gained a year every January 1. Some traditional East Asian contexts still use lunar-calendar reckoning. This calculator uses the Western system the WHO and most jurisdictions employ.

Practical uses

Resume math (years of experience to a precise date), insurance underwriting, school admission cut-offs, retirement countdowns, child-development milestones, and the occasional pub-quiz fact about how many days you've been alive.

Sources & references

Authoritative references behind the math, constants, and tables on this page. Verified by Buğra Sözeri on the dates shown and re-checked at every deploy.

Gregorian calendar — papal bull Inter gravissimas (1582) — Origin of the leap-year rules (divisible by 4, except 100, except 400) that the calculator handles(as of 2026-05-21)
ISO 8601:2019 — Date and time representations — Date format used by the widget input and output(as of 2026-05-21)
South Korea — Act on Age Calculation and Indication (2023) — Background on Korea's 2023 switch from "Korean age" to international counting referenced in the about section(as of 2026-05-21)

Related guide

Why does “completed years” differ from “current year” counts, and how do leap years, time zones, and cultural conventions shift the answer? The age calculation guide walks through each method.

Read: Age calculation methods →