Age calculator
Age is counted in whole calendar years, then whole months, then the remaining days: someone born on 15 May 1990 is 36 years, 3 months and 8 days old on 23 August 2026. The same page gives days, hours and seconds alive, the gap between two birth dates, and the age on seven other planets.
How to work out an age
Month arithmetic is where these calculators disagree with each other. From 31 January to 1 March is one month and one day here, because adding a month to 31 January lands on 28 February, the last day that exists, and one more day gets you to 1 March. Any other rule produces an impossible date somewhere along the way.
The day, hour and second totals carry no such convention, which is why they never disagree with anything: they subtract, leap days included, so forty years is 14,610 days and not 14,600. Hours are the unit where a lifetime starts to feel finite. A year is 8,766 hours on the 365.25-day average, so a forty-year-old has had about 350,000 of them and, at eight hours a night, has slept through around 117,000. Of the roughly 233,000 hours left awake, a conventional forty-hour week over forty years accounts for something like 80,000. None of that is a moral instruction, but it is a different framing from a birthday, and the arithmetic is at least honest about where the time goes.
The nominal age shown alongside is the Korean one, best known of the East Asian reckonings: one at birth, then a year added every 1 January instead of on the birthday. Counting from one names the year of life you are in, not the years completed, which is the same logic that puts the first floor at ground level across much of Europe. The Chinese count, 虚岁, works that way too but steps at Lunar New Year, somewhere between 21 January and 20 February. That count is not worked out here. Because the two step at different moments they part company by a year for a stretch of every year, and both the stretch and the direction depend on where the birth date sits: for anyone born after a Lunar New Year, which is most people, the Korean figure runs a year ahead from 1 January until the next one, and for anyone born inside those few January weeks it is the other way round for the rest of the year. So the number here is 虚岁 only some of the time, and it is not labelled as it. Mainland China has used international age officially for decades and the nominal count survives in astrology, in traditional contexts and among older speakers; South Korea moved to international age in law in 2023, with the same afterlife in speech.
The half-plus-seven mode is folklore with tidy arithmetic and nothing else behind it. The range widens by a year and a half for every year of age, and it collapses at fourteen, where the two bounds meet on a single year; below fourteen they cross and the rule permits nobody at all. The planets mode is a division: days alive over each orbital period, which is why a year on Mercury is 88 days and one on Neptune is 164.8 Earth years. Pluto, at 248 years, is missing for the reason it left the textbooks: it has been a dwarf planet since 2006.
What people use it for
- Filling in a form that wants an age to the day
- Settling which of two people is older, and by how much
- Working out a sibling age gap
- Checking the gap between two partners
- Counting how many days old someone is
- Marking a 10,000-day milestone
- Working out how many weeks old a baby is
- Filling in a developmental checklist by age in months
- Quoting a lifetime in hours
- Finding the date you turn a billion seconds old
- Checking a birth date against an age threshold on a given day
- Converting a Korean age to a Western one
- Reading a Korean nominal age, and knowing when it parts company with the Chinese one
- Checking the arithmetic behind the half-plus-seven saying
- Comparing an Earth age against Mars and Mercury years
Questions
Complete years first, then complete months, then the days left over. That is how old someone is exactly rather than to the nearest year, and the day before a birthday they are still the previous age.
Put both birth dates into the two-dates mode. The difference comes back in years, months and days, and it does not matter which you enter first: how much older one is than the other is the same number either way round.
Enter your birth date and read the day total: the count from then to today, leap days included.
Leap days. Forty years is 14,610 days rather than 14,600, because ten 29 Februaries fall inside it.
At 27 years and about four and a half months. It is always 138 or 139 days past the twenty-seventh anniversary, and which of the two depends on how many 29 Februaries fell inside the span.
Days alive times 24, which the hours row gives you directly. A year is 8,766 hours on the 365.25-day average, or 8,760 in a common year, so a forty-year-old is somewhere around 350,000 hours old.
At eight hours a night, about a third of the total: roughly 117,000 by forty. Of the 233,000 or so waking hours, a forty-hour week over a forty-year career accounts for something like 80,000, which is a little over a third of them.
Days since birth divided by seven, rounded down to completed weeks. Most newborn guidance is written in weeks because development changes that fast.
Neither, and the mix-up is common enough to move an appointment. Four weeks is 28 days, and only a common-year February is that short. Twelve weeks is 84 days against 89 to 92 for three calendar months, so the two readings sit five to eight days apart.
Subtract the weeks born early from the chronological age. A baby born at 32 weeks is eight weeks early, so at 20 weeks old their corrected age is 12 weeks.
It falls back to 28 February in a common year for the age and next-birthday figures, and returns to the 29th in the next leap year. The legal answer is a separate question, and no calendar rule settles it: the birthday calculator sets out which convention each of its tabs uses and why.
Yes. Change the second date to any day and you get the age as of that day, which is what forms and eligibility rules usually want.
On their eighteenth birthday in most jurisdictions. A historical rule using the previous day was abolished in England in 1969.
No. It will tell you whether someone was old enough on a given day, which is what a minimum-age check needs, but it is arithmetic on a date you typed in. Real verification means checking a document against a person.
Both are East Asian nominal counts that make you one at birth. Korean age then adds a year every 1 January, so a baby born on 31 December is two the following day. The Chinese count, 虚岁, steps at Lunar New Year instead, which falls between 21 January and 20 February.
No, and it is worth being blunt about it: the figure here is the Korean one and it steps on 1 January. Lunar New Year falls between 21 January and 20 February, so for part of every year the two counts are one apart. If you were born after a Lunar New Year, which covers most people, the Korean number runs a year ahead of 虚岁 from each 1 January until the next New Year, some five to seven weeks. If you were born inside those weeks instead, it is 虚岁 that runs ahead, and for the rest of the year. Mainland China has used international age officially for decades in any case.
At 31 years and 251 days, about 31 years and eight months. A year is roughly 31,557,600 seconds on the 365.25-day average, and a common year is exactly 31,536,000.
Divide your age by two and add seven for the youngest bound, then reverse it for the oldest: at 30 that gives 22 to 46. The dating rule, or the creepiness rule as it also gets called, is at least symmetric, so anyone whose range you fall inside falls inside yours. It is folklore all the same, with no research under it.
About 0.53 times your Earth age, since a Martian year is 687 Earth days. Mercury goes the other way at 4.15 times, its year being 88 days. Venus is the strange one: 243 Earth days to turn once against 225 to go round, so a day there outlasts a year.
Because it has been a dwarf planet since 2006 and the list holds the eight planets. Its orbit takes 248 Earth years, so a long human life comes to barely a third of one Plutonian year.
No. The gap between two birth dates is fixed. What changes is its ratio to the younger person’s age, which is why the same relationship gap feels wide at twenty and unremarkable at sixty. Whether it is acceptable is not a question arithmetic can answer.
Not here. The count is date to date, so a birth at 23:50 and one at 00:10 the next morning are a whole day apart in these figures.