Your exact age in years, months and days — plus every other unit at once, the age you would be on any past or future date, and the traditional Korean age. No date is sent anywhere; the whole thing runs in your browser.
Age Calculator
LiveSet a future date to find an age on a deadline, or a past one to check an age at the time of an event — eligibility rules, school cut-offs and legal thresholds all turn on a date rather than today.
How the calculation works
Age in years, months and days is not a single subtraction. Months have different lengths, so the arithmetic has to walk the calendar rather than treat dates as numbers:
| Step | What happens |
|---|---|
| 1. Years | Count completed birthday anniversaries. If this year's birthday has not arrived yet, subtract one |
| 2. Months | From that anniversary, step forward one month at a time while the result is still on or before the reference date |
| 3. Days | Count the remaining days from the last monthly mark to the reference date |
Subtracting the date parts and borrowing from the previous month looks simpler and gives the right answer most of the time. Then someone born on 31 January checks their age on 1 March: the day subtraction gives 1 − 31 = −30, the borrow adds February's 28 days, and the result is minus two days. Several well-known calculators return exactly that. Walking anniversaries forward and clamping to the end of a short month avoids it entirely.
The 29 February problem
Roughly one person in 1,461 is born on a leap day, and three years out of four their birthday does not exist. When it does not, what date do they turn a year older?
| Jurisdiction | Birthday falls on | Where this matters |
|---|---|---|
| England & Wales | 1 March | Reaching 18 for legal purposes |
| Most US states | 1 March | Driving licences, drinking age |
| New Zealand, Taiwan | 28 February | Statutory age of majority |
| Hong Kong | 1 March | Age of majority ordinance |
This calculator uses 28 February in non-leap years, which is the convention most calendar software follows and which keeps the birthday inside the same month. The difference is one day and only appears in three years out of four, but if a legal threshold is involved, check the rule for your jurisdiction rather than any calculator.
Korean age: three systems, one law change
Korea used a counting system in which a newborn is one year old at birth and everyone gains a year on 1 January rather than on their own birthday. On 28 June 2023 South Korea standardised the international system for all legal and administrative purposes, but the traditional count is still used socially and the counting-year system remains in some laws.
| System | Formula | Still used for |
|---|---|---|
| International (만 나이) | Completed years since birth | All legal and administrative matters since June 2023 |
| Traditional (세는나이) | Current year − birth year + 1 | Everyday conversation, social hierarchy, media |
| Counting year (연 나이) | Current year − birth year | Military conscription, school entry, some statutes |
Corrected age for premature babies
A baby born before 40 weeks is measured against two clocks. Chronological age counts from birth; corrected age subtracts the weeks the baby arrived early, and it is the one developmental milestones are assessed against.
| Term | Definition |
|---|---|
| Gestational age | Weeks of pregnancy at birth, counted from the last menstrual period. Full term is 39–40 weeks |
| Chronological age | Time since birth, the same measure used for everyone else |
| Corrected age | Chronological age minus the weeks born before 40. A baby born at 32 weeks is corrected by 8 weeks |
Corrected age is used until roughly two to three years, after which the difference stops being clinically meaningful for most children. A ten-month-old born at 30 weeks has a corrected age of about seven and a half months — and should be compared with seven-month milestones, not ten-month ones.
This is general information, not medical advice. Correction periods and milestone expectations are set by a paediatrician who knows the individual child.
Age thresholds that actually matter
Most searches for an exact age are driven by a rule with a date attached. The common ones:
| Threshold | Age | Note |
|---|---|---|
| Legal adulthood (most countries) | 18 | 21 in some US contexts, 20 in Japan until 2022, now 18 |
| US drinking age | 21 | Uniform across states since 1984 |
| Full US Social Security retirement | 67 | For anyone born 1960 or later. 66 and a fraction for 1955–59 |
| Earliest Social Security claim | 62 | Permanently reduces the monthly benefit by up to 30% |
| IRS required minimum distributions | 73 | Rising to 75 for those born 1960 or later |
| Medicare eligibility | 65 | Enrolment window opens three months before the birthday |
Sources: East Asian age reckoning and the June 2023 Korean statute · Social Security Administration full retirement age tables · SECURE 2.0 Act RMD schedule · national age-of-majority legislation. Cited for the specific figures above; verify anything with a legal consequence against the current rule for your jurisdiction.
Age reckoning elsewhere
Korea is the best-known case and not the only one. Several systems count differently, and a few still matter for legal or religious purposes:
| System | How it counts | Where it still applies |
|---|---|---|
| International | Completed years since birth | Everywhere for legal purposes. What this calculator gives by default |
| Traditional East Asian | Born at 1, plus one at Lunar New Year | Korea until 2023, and still culturally in parts of China, Japan and Vietnam |
| Korean year age | Current year minus birth year | Survives in Korea for school entry and military conscription |
| Hijri age | Completed lunar years | Some religious and legal contexts. A lunar year is about 354 days, so Hijri age runs roughly 3% higher |
| Nearest birthday | Rounded to the closest one | Life insurance underwriting in several markets. Can add a year up to six months early |
The insurance case surprises people. Many life policies price on “age nearest birthday”, so someone seven months past their 39th birthday is priced as 40. Buying a month earlier can cost noticeably less for identical cover, and nothing on the application says so.
How the law defines the moment you turn a year older
Most people assume you become a year older on your birthday. In several jurisdictions the law says otherwise:
| Jurisdiction | You attain an age | Consequence |
|---|---|---|
| England and Wales | At the first moment of your birthday | Family Law Reform Act 1969, s.9. Midnight, not the hour of birth |
| United States | Generally the day before, at common law | Largely superseded by statute, but the rule survives in some contexts |
| 29 February births | 1 March in most jurisdictions | England and Wales treat a leapling as attaining age on 1 March in common years |
| New Zealand | Beginning of the birthday | Age of Majority Act 1970 states it explicitly |
Common mistakes
Frequently asked questions
How do I calculate my exact age?
Count completed birthday anniversaries for the years, step forward month by month from that anniversary, then count the days remaining. Dividing total days by 365 is the common shortcut and it drifts by roughly a day every four years because of leap years.
What is my Korean age?
Traditional Korean age is the current year minus your birth year, plus one — everyone is one at birth and gains a year on 1 January. The calculator shows this alongside the counting-year system and your international age. South Korea moved to the international system for legal purposes in June 2023, but the traditional count is still used socially.
When is the birthday of someone born on 29 February?
It depends on the jurisdiction. England, Wales and most US states treat 1 March as the day a leap-day baby turns a year older; New Zealand and Taiwan use 28 February. This calculator uses 28 February, which keeps the birthday in the same month and matches most calendar software. Where a legal threshold is involved, check the rule that applies to you.
What is corrected age and when should I use it?
Corrected age subtracts the weeks a baby was born before 40 from their chronological age. It is the measure developmental milestones are assessed against, and it is generally used until two to three years. A baby born at 32 weeks who is six months old chronologically has a corrected age of about four months.
Can I find my age on a future date?
Yes — set the second date field to any date, past or future. This answers the questions people actually have: how old will I be at a deadline, was I old enough on a given date, will a child meet a school cut-off.
How many days old am I?
The calculator shows the total in days, weeks, hours, minutes and seconds at the same time. As a rough guide, 10,000 days is about 27 years and 4 months, and a billion seconds is a little under 32 years.
Why does my age differ by a day from another calculator?
Usually time zones or month arithmetic. Some tools calculate in UTC, so a birthday near midnight shifts by a day depending on where you are; this one uses your local time zone. The other cause is how a tool handles month ends — 31 January to 1 March is where the differences appear.
Is my date of birth stored?
No. Everything runs in your browser with no server request, and works offline once the page has loaded. Nothing is written to disk and nothing persists after you close the tab.
Sources
- Republic of Korea, Act on Age Counting and Indication. Promulgated December 2022, in force 28 June 2023. Standardised legal and administrative age on the international system, ending the routine use of traditional Korean age.
- Family Law Reform Act 1969 (England and Wales), section 9. A person attains a particular age at the first moment of the relevant birthday — the statute that replaced the older common-law rule of the day before.
- American Academy of Pediatrics. Guidance on corrected age for preterm infants: chronological age minus the number of weeks born before 40, applied to developmental milestones until around 24 months.
- World Health Organization. Child growth standards, which are plotted against corrected age for infants born preterm rather than against date of birth.
- ISO 8601:2019. Date representation. The YYYY-MM-DD form used throughout, and the proleptic Gregorian calendar this page assumes.
- Dershowitz N, Reingold EM. Calendrical Calculations. Cambridge University Press. The reference for lunar and lunisolar calendars, including why a Hijri age runs about 3% higher than a Gregorian one.
Age is computed by walking calendar anniversaries from the date of birth rather than by dividing elapsed days, which is the only method that stays correct across leap years. Anniversaries are anchored to the original date, so 29 February 2000 to 29 February 2024 is exactly 24 years — adding a year at a time clamps to the 28th on the first step and never recovers.
Related calculators
See the full list of Date & Time calculators, or try:
- Date Difference Calculator — days between any two dates
- Age Difference Calculator — the gap between two people
- Leap Year Calculator — which years have a 29 February
- Generation Calculator — which generation a birth year falls in
- Pet Age Calculator — dog and cat years, done properly
- Retirement Calculator — the age the money runs to