Age & Date Calculator
Korean legal age, D-day, 100-day and yearly anniversaries, the span between two dates, N days or months later, and business days excluding holidays.
Result
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Business days in a period
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N business days later / earlier
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Public holidays, substitute holidays and confirmed temporary holidays and election days (1900–2100). Temporary holidays declared in future are unknown, so check government announcements. The file is built in this browser and saved directly; import it into Google, Apple or Outlook calendars.
Summary by year
Dates
Lay a rotating shift pattern (for example a 6- or 8-day cycle) onto a calendar and download it as an .ics file. Google Calendar cannot repeat cycles like this, so every working day is written out as its own all-day event.
One letter per day: D (day) · E (evening) · N (night) · O (off). Example: DDNNOO (up to 60 days). Nothing you type is sent to the server.
Calendar
This month
Calendar file (.ics)
For reference only; it has no legal effect. Your employer’s official roster (crew assignment, swaps, leave) may differ, so follow the confirmed schedule. Public holidays include only those already announced. The file is created in this browser and saved directly.
"Today" is based on Korea Standard Time (KST). Dates you enter are never sent to a server.
Rules used
Age = this year − birth year, minus 1 if this year's birthday has not come yet (Korea's standard age in law and administration since 28 June 2023). The year-based age (this year − birth year) and the traditional count are shown too. A 29 February birthday is treated as turning a year older on 1 March in common years. When the result month lacks the day (31 January + 1 month), the last day of that month is used (28 or 29 February).
Business days
Excludes Saturdays, Sundays and public holidays (including substitute holidays). Holidays follow current law plus the temporary holidays and election days confirmed so far; ones announced later are not reflected. Banks and offices may differ, so confirm important deadlines. Works for years 1900–2100.
Split what you need to study (pages, lectures, problems) evenly over the days left before the exam. Skip rest days and holidays and keep the last few days for review. Print the plan or download it as a calendar file.
The exam day itself is not part of the plan. Leftover units go to the earlier days, one each, so it is easier to catch up. Nothing you enter goes to a server.
Not medical advice. This is an estimate from a standard formula; the real gestational age and due date are set by ultrasound, and your clinic's dates take priority. Nothing you enter is saved or sent.
Due date = first day of last period + 280 days (adjusted if the cycle is not 28 days); from conception it is conception + 266 days. Pregnancy months count 4 weeks as one month. Check-up timing is general guidance and varies by person.
Pick a date and place to see sunrise, sunset, solar noon, day length, civil twilight, golden hour, moonrise/moonset and the moon phase (illumination, next full/new moon). Your location never leaves the browser.
A simplified astronomical calculation: sunrise/sunset within 1–2 minutes, the moon within a few minutes. For daily life and photo planning, not navigation. Terrain (hills, buildings) is ignored. Times use the place’s own time zone, including daylight saving.
FAQ
What is the difference between "man" age and year-based age?
Man (international) age increases on your birthday; year-based age increases every January regardless (this year − birth year). Some laws, such as military service and youth protection, still use year-based age.
Is my birth date stored?
No. Everything is calculated in your browser and nothing is transmitted.
Does D-day include today?
By default it shows the days remaining excluding today. Turn on "Count the start day as day 1" to count today as day 1, which adds one day (useful for anniversaries).
How to use this tool
Use it for any date calculation: age, anniversaries, days remaining. The tabs cover international (man) age, D-day, 100-day and yearly anniversaries, the span between two dates, N days later, business days, public holidays, shift schedules, pregnancy weeks, sunrise and sunset, and a study plan. Enter a base date and the result appears immediately.
Frequently asked questions
What is the difference between Korean age and international age?
Since June 28, 2023, Korean law and administration use international ("man") age: the number of full years since birth. Enter a birth date to get it instantly.
How are D-day and 100-day anniversaries calculated?
The Korean convention counts the start date as day 1. You can see the dates for day 100, 200, the first anniversary, and more at once.
Can I count business days without holidays?
Yes. The business-day tab skips weekends and public holidays and can also find the date N business days ahead.
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