Age
Calculate exact age in years, months, days, hours. See your age on other planets, countdown to next birthday, and compare two people.
Age sounds trivial to calculate until you notice the edges. February 28 to March 1 is one day, except in leap years when it's two. "Three months" depends on which three months. A year on Mars is 687 Earth days. This calculator handles all of that and gives you the answer in every unit you might actually want.
Useful for the obvious case ('how old am I, exactly?'), and also for legal paperwork, retirement math ('how many days until I turn 65?'), planning kids' milestones, and mild curiosities like your age on Mars.
How age is calculated
The standard method — sometimes called Western age — increments by 1 every time you pass your birthday. Born March 15, 1990? You became 1 on March 15, 1991. You'll be 36 on March 15, 2026, not before.
The 'years / months / days' breakdown computes the largest unit first: count whole years between the two dates, then whole months past that anniversary, then remaining days. February 28 to March 1 is 0 years, 0 months, 1 day in normal years. In a leap year it's 2 days because February has 29.
Total units (weeks, days, hours, minutes, seconds) are just the raw elapsed time divided. Days = floor((target − birth) / 86,400,000 ms). Leap seconds and DST don't materially affect this at human-age scale.
Δy = target.year − birth.year (adjusted if anniversary not yet passed)
- birth
- Date of birth (at 00:00 UTC by default)
- target
- Date to measure age at (defaults to now)
- Δy / Δm / Δd
- Years / months / days difference
Practical examples
Exact age today
Setup: Born March 15, 1990. Today is April 21, 2026.
36 years, 1 month, 6 days. Or: 13,186 days. Or: 316,464 hours. Or: 1.14 Billion seconds.
Takeaway: The 'years + months + days' is the human-friendly answer. Total days is useful for legal docs or milestones ('I'll have been alive for 20,000 days on...'). Total seconds is fun to show kids.
Age at retirement
Setup: Born July 3, 1965. Retirement eligibility: 67. What's the exact retirement date?
July 3, 2032. Days from today (Apr 21, 2026) until retirement: 2,266 days.
Takeaway: Use the 'Age on date' field to project forward. Helps for retirement planning, visa timelines (must be 18 on date of arrival), or scheduled milestones.
Two-person age difference
Setup: Person A born Jan 1, 1990. Person B born March 15, 1995.
Difference: 5 years, 2 months, 14 days. Or 1,899 days.
Takeaway: The difference is constant over time — a 5-year gap at age 1 is the same 5-year gap at age 80. It feels bigger when you're young because it's a larger percentage of your life.
Practical notes
- Birthdays in leap years (Feb 29): if you're born on a leap day, most countries default your legal birthday to Feb 28 or March 1 in non-leap years. Check your country's civil registry rules.
- Time zones matter for precise age. A baby born at 1 AM in Tokyo is still 'not born yet' by New York time (it's still previous-day evening there). For legal age thresholds, the birth certificate's stated time zone is what counts.
- Korean age (나이, the traditional system) adds a year at birth and another at every Lunar New Year — so a Korean 'two-year-old' can be a Western newborn. Since 2023, Korea officially uses international age for legal and administrative purposes.
- Fractional years are common in medical, legal, and demographic contexts: '6.3 years old' rather than '6 years 4 months'. Convert: total days / 365.25.
Limits of this calculator
This tool computes chronological age only — the number of years since birth. Medical biological age (cardiovascular fitness, telomere length, cognitive scoring) is a different measurement and requires clinical testing.
For life events that happened before birth, or age ranges of objects (e.g. age of a building, age of a fossil), you want a duration calculator, not an age one. The math is identical but the framing matters: birth-based age implies a specific start event.
The planetary ages shown are based on each planet's sidereal orbital period in Earth days. They're fun but don't correspond to anything physical about you — your body doesn't age faster on Mercury. It's just the number of Mercury years that have passed since your birth.
Frequently asked questions
Why does month count sometimes seem off?▾
Because 'a month' has variable length (28-31 days). 'Feb 28 to Mar 31' can be read as 'one month and three days' or 'one month and two days' depending on convention. We use the convention: same-day anniversary in a later month counts as a full month. So Feb 28 → Mar 28 is one month, Mar 28 → Mar 31 adds three more days.
How accurate are planetary ages?▾
Very accurate for Mercury, Venus, Earth, Mars, Jupiter, and Saturn — we use sidereal orbital periods measured by NASA. A 'Mars year' = 686.97 Earth days; 'Mercury year' = 87.97 days. The display shows total elapsed / that period, rounded to 2 decimals.
Does this account for leap years?▾
Yes. The years/months/days breakdown uses real calendar math, so Feb 29 is counted only when it exists. Total days uses actual milliseconds elapsed, which naturally includes any leap days between the two dates.
What if I don't know my exact birth date?▾
For approximate ages, use the first day of the month you think you were born, or the middle of the year if you only remember the year. For legal purposes, only the date on your birth certificate counts — there are bureaucratic procedures in most countries to correct incorrect registrations.
Can this predict my death or life expectancy?▾
No — this is purely a math tool. Life expectancy depends on country, sex, socioeconomic factors, genetics, and lifestyle. As of 2024, global average life expectancy is ~73 years; in the US ~79; in Japan and Switzerland ~84. Subtract your current age to get the statistical remaining time, but remember: those are averages, not predictions.
Sources
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