Age Calculator
Returns your age broken into completed years, months, and days. The years figure is the one people want and it is not simply the difference in year numbers, because whether the birthday has occurred yet this year changes the answer.
How to use it
- Enter your birth date.
- Read the completed years, months, and remaining days.
- Nothing is transmitted, which matters given a birth date is identifying information.
Age is completed years, not a year subtraction
Subtracting birth year from current year gives the right answer only after the birthday has passed. Someone born in December 1990 is 34 in January 2026, not 36, because the 2026 birthday has not happened.
The correct method takes the year difference and subtracts one if the current month and day fall before the birth month and day. This is the borrow-and-carry logic that makes the calculation slightly more than arithmetic.
Months and days work the same way. From 15 March 1990 to 10 January 2026 is 35 years, 9 months, and 26 days: the year borrows to give 35, the month borrows from that to give 9, and the days are counted from 15 December to 10 January. Because the borrow depends on the length of the preceding month, the day count is not a fixed figure, which is why two people with birthdays a day apart can show different day remainders.
February 29 birthdays
Roughly one person in 1,461 is born on a leap day, and three years in four their exact birth date does not exist.
Conventions differ and are genuinely inconsistent. Most computer systems roll to 1 March, treating the anniversary as the day after 28 February. Many legal frameworks use 28 February, on the reasoning that the anniversary occurs within the same month. Some jurisdictions specify for particular purposes — the age of majority, driving eligibility, insurance — and the answers do not always agree with each other.
For anything with a legal threshold attached the applicable rule matters, so it is worth checking rather than assuming. For a personal age figure the difference is one day and of no practical consequence.
Age reckoning is not universal
The system used here — completed years since birth, incrementing on the birthday — is the international standard, but it is not the only one that has been in use.
The traditional East Asian system counted a person as one at birth and incremented everyone at the lunar new year, so a baby born shortly before new year could be two within days. South Korea used a variant, counting from one at birth and incrementing on 1 January, which typically made Korean ages one or two years higher than international ages. South Korea standardised on the international system in 2023, though the traditional count survives in conversation.
This is worth knowing when reading historical records, genealogical documents, or older census data, where a stated age may not mean completed years since birth. It is a common source of apparent inconsistency in family history research.
Where exact age matters
For most purposes the years figure is enough. Several contexts need the finer breakdown.
- Paediatric medicine, where growth charts, dosing, and developmental milestones are indexed by age in months, and a two-month difference at eighteen months is clinically meaningful.
- Insurance underwriting, where many policies price on age at nearest birthday rather than last, so being seven months past a birthday puts you in the next bracket.
- Sports eligibility, where cut-off dates create competitive age groups and a few days determines which group applies for a season.
- School enrolment, which uses a fixed cut-off date rather than the school year start, so late-summer birthdays fall either side depending on jurisdiction.
- Pension and retirement thresholds, where eligibility is often defined to a specific month rather than a year.
At a glance
| Method | Completed years, months, and days with borrow logic |
|---|---|
| Leap day | Handled by calendar arithmetic |
| Convention | International reckoning, incrementing on the birthday |
| Transmitted | Nothing, the birth date stays in the page |
Frequently asked questions
Why can I not just subtract the years?
Because it only works after the birthday has passed. Someone born in December 1990 is 34 in January 2026, not 36.
How are February 29 birthdays handled?
Conventions differ. Most software rolls to 1 March; many legal frameworks use 28 February. For legal thresholds, check the rule that applies.
Why does the day remainder look odd?
Because the month borrow uses the length of the preceding month, which varies. Two nearby birthdays can produce different day counts.
Is my birth date sent anywhere?
No. The calculation runs in the page, which matters because a birth date is identifying information.
Read more
Working with dates and time — Days are exact, months are a convention, and two hours a year do not exist or happen twice.