Does this calculate 만 나이 or 세는 나이?

만 나이 (calendar/international age), computed by subtracting your birth date from the reference date component by component. This matches Korea's legal default since the 만 나이 통일법 took effect on 28 June 2023. It does not compute 세는 나이 (counting age) or the calendar-year-based 연 나이 still used in a few specific statutes — those need a different, Korea-specific calculator.

What happens if I was born on February 29?

In non-leap years, this tool doesn't roll your age over until 1 March, not 28 February. For example, someone born 29 February 2000 still shows as 24 years, 11 months, 30 days on 28 February 2025, and reaches exactly 25 years, 0 months, 0 days only on 1 March 2025. This matches the UK's statutory rule (1 March, per the Age of Legal Capacity (Scotland) Act 1991) and Maine's, but not everywhere — California and Nevada instead treat 28 February itself as the anniversary in non-leap years. If that distinction matters legally for you, check the specific rule for your jurisdiction rather than relying on this default.

What does the tool do with a birthday on the 31st when the month is shorter?

It clamps to the last day of the shorter month rather than spilling into the next one. A birthday on 31 January has no anniversary in February, so the tool treats 28 February (29 in a leap year) as the one-month mark, and counts days forward from there. Born 31 January 2000 and checking on 1 March 2025, you get 25 years, 1 month, 1 day. The visible consequence is that births on 29, 30 and 31 January all land on the same anchor and read identically in early March. That is the standard convention, not a universal truth — some legal systems roll such an anniversary forward to 1 March instead, so if a deadline or a legal age turns on it, check the rule that actually applies to you.

Does it upload my birth date to a server?

No. Every calculation runs entirely inside your browser using plain JavaScript Date arithmetic. Your birth date is never sent anywhere and the tool keeps working with no internet connection at all.

Can I calculate age at a specific past or future date instead of today?

Yes. Fill in the 'Age at Date' field with any date — past or future — and every result (the years/months/days breakdown, totals, and the next-birthday countdown) recalculates relative to that date instead of today.

Why don't the total hours or total months exactly match what I'd get dividing total days by 24 or 30?

Total months is computed from the calendar breakdown itself (years x 12 + months), not from dividing days by 30, so it stays accurate to actual month lengths. Total hours is total days multiplied by 24 — and total days is deliberately rounded to whole calendar days so daylight-saving transitions don't shift the count by one, which means the hours figure re-introduces the assumption of a uniform 24-hour day. If you've lived through DST changes, your true elapsed hours differ from this total by roughly one hour per transition.

🎂 Age Calculator

Toolio's Age Calculator computes calendar age — years, months, and days broken out the way people naturally say their age — rather than dividing total elapsed days by 365. It matches Korea's current legal standard, 만 나이 (international/calendar age), which has been the default interpretation of 'age' under Korean civil and administrative law since the 만 나이 통일법 took effect on 28 June 2023 (promulgated 27 December 2022). It does not compute either of Korea's other two age systems — 세는 나이 (counting age) or the calendar-year-based 연 나이 still used in a handful of statutes — and it has one narrow, reproducible display bug around birthdays on the 31st crossing into early March, detailed below.

Toolio's Age Calculator subtracts a birth date from a reference date (today by default) to report exact age in whole years, months, and days, plus total days, weeks, hours, and months, entirely offline in your browser.

Date Inputs

Date of Birth

Age at Date

Leave "Age at Date" empty to use today.

Private by design. This tool runs entirely in your browser — nothing you enter is uploaded or stored, and it works offline.

About

The core algorithm is calendar subtraction with borrowing, the same method most people do mentally: subtract the birth year, month, and day from the reference year, month, and day component by component; if the day difference goes negative, borrow the number of days in the month before the reference month and subtract one from the month count; if the month difference is then negative, borrow twelve and subtract one from the year count. Worked all the way through with real numbers: someone born 15 May 1990, checked on 15 July 2026, comes out to exactly 36 years, 2 months, 0 days — with total days of 13,210, total weeks of 1,887, total hours of 317,040, total months of 434, and 304 days remaining until the next birthday.

On the 만 나이 question specifically: before mid-2023, Korea routinely used three overlapping age systems in daily life — 세는 나이 (everyone is 1 at birth and gains a year every New Year's Day, regardless of birth month), 연 나이 (age based on the current calendar year minus birth year, still used in specific statutes such as those governing alcohol, tobacco, and military conscription), and 만 나이 (the international standard, counted from actual birth date). The 만 나이 통일법 — amendments to the 민법 (Civil Act) and 행정기본법 (Framework Act on Administrative Law) — was promulgated 27 December 2022 and took effect 28 June 2023, making 만 나이 the default reading of 'age' in laws, contracts, and official documents unless a specific rule says otherwise. This tool always computes 만 나이-style calendar age; it does not offer a 세는 나이 or 연 나이 mode. Toolio's separate Korean Age Calculator exists specifically for those two.

February 29 birthdays surface a genuine ambiguity that this tool resolves in one particular direction. Someone born 29 February 2000, checked on 28 February 2025 (the last day of February in that non-leap year), still shows as 24 years, 11 months, 30 days — one day short of turning 25. The tool only rolls over to exactly 25 years, 0 months, 0 days the following day, 1 March 2025. In effect, this calculator treats 1 March as a leap-day baby's anniversary in non-leap years — which matches the statutory rule in the UK (the Age of Legal Capacity (Scotland) Act 1991 explicitly names 1 March as the relevant anniversary in non-leap years) and in Maine, but not every jurisdiction agrees: California treats 29 February and the day immediately before it as one day, so age-linked rights there apply from 28 February in non-leap years, and Nevada's driver-licensing rules do the same. If your situation depends on a specific jurisdiction's leap-day rule, verify against that jurisdiction's own statute rather than this tool's default rollover date.

Month-end date arithmetic is famously ambiguous, and this tool has to take a position on it. 'Jan 31 plus one month' has no single correct answer, because February has no 31st. JavaScript's own naive date math overflows forward: ask setMonth to add a month to 31 January and it lands on 3 March, not 28 February, because day 31 does not exist in February and spills into the next month. This tool refuses that overflow. It never adds months at all — it subtracts the two dates you give it, component by component, and when the day count needs to borrow from the month before your reference date, it first clamps your birth day to that month's length. So 31 January plus one month resolves to 28 February, and someone born on 31 January 2000, checked on 1 March 2025, reads as 25 years, 1 month, 1 day. The trade-off of that choice is worth knowing: births on the 29th, 30th and 31st of January all clamp to the same 28 February anchor, so in early March they produce identical breakdowns. That is the conventional answer, and it is the one banks and payroll systems generally use, but it is a convention rather than a fact of the calendar.

Finally, the total-hours figure is derived by multiplying the total-days figure by 24, and total-days itself is computed by rounding the millisecond difference between the two dates to the nearest whole day specifically so that daylight-saving-time transitions (23-hour or 25-hour calendar days) don't throw the day count off by one. But because total-hours is then just days times 24, it silently reinstates the assumption that every calendar day had exactly 24 real hours — so if you've lived through DST transitions, your true elapsed hours differ from the displayed total by roughly one hour per transition you've experienced.

How to use

Enter your date of birth in the 'Date of Birth' field.
Leave 'Age at Date' empty to measure against today, or set any past or future date to see your age at that specific point in time.
Click 'Calculate' (or press Enter while focused on the birth date field) to see the breakdown instantly.
Read the primary result (years, months, days) plus the totals grid: total days, total weeks, total hours, and total months, all derived from the same underlying date subtraction.
Check the countdown line for days remaining until the next birthday, calculated from the reference date you set.
Click 'Copy' to copy the age text to your clipboard, or 'Reset' to clear both fields and start over.

FAQ

Does this calculate 만 나이 or 세는 나이?: 만 나이 (calendar/international age), computed by subtracting your birth date from the reference date component by component. This matches Korea's legal default since the 만 나이 통일법 took effect on 28 June 2023. It does not compute 세는 나이 (counting age) or the calendar-year-based 연 나이 still used in a few specific statutes — those need a different, Korea-specific calculator.
What happens if I was born on February 29?: In non-leap years, this tool doesn't roll your age over until 1 March, not 28 February. For example, someone born 29 February 2000 still shows as 24 years, 11 months, 30 days on 28 February 2025, and reaches exactly 25 years, 0 months, 0 days only on 1 March 2025. This matches the UK's statutory rule (1 March, per the Age of Legal Capacity (Scotland) Act 1991) and Maine's, but not everywhere — California and Nevada instead treat 28 February itself as the anniversary in non-leap years. If that distinction matters legally for you, check the specific rule for your jurisdiction rather than relying on this default.
What does the tool do with a birthday on the 31st when the month is shorter?: It clamps to the last day of the shorter month rather than spilling into the next one. A birthday on 31 January has no anniversary in February, so the tool treats 28 February (29 in a leap year) as the one-month mark, and counts days forward from there. Born 31 January 2000 and checking on 1 March 2025, you get 25 years, 1 month, 1 day. The visible consequence is that births on 29, 30 and 31 January all land on the same anchor and read identically in early March. That is the standard convention, not a universal truth — some legal systems roll such an anniversary forward to 1 March instead, so if a deadline or a legal age turns on it, check the rule that actually applies to you.
Does it upload my birth date to a server?: No. Every calculation runs entirely inside your browser using plain JavaScript Date arithmetic. Your birth date is never sent anywhere and the tool keeps working with no internet connection at all.
Can I calculate age at a specific past or future date instead of today?: Yes. Fill in the 'Age at Date' field with any date — past or future — and every result (the years/months/days breakdown, totals, and the next-birthday countdown) recalculates relative to that date instead of today.
Why don't the total hours or total months exactly match what I'd get dividing total days by 24 or 30?: Total months is computed from the calendar breakdown itself (years x 12 + months), not from dividing days by 30, so it stays accurate to actual month lengths. Total hours is total days multiplied by 24 — and total days is deliberately rounded to whole calendar days so daylight-saving transitions don't shift the count by one, which means the hours figure re-introduces the assumption of a uniform 24-hour day. If you've lived through DST changes, your true elapsed hours differ from this total by roughly one hour per transition.