Month math clamps to the last day
Adding one month to January 31 gives February 28, not March 3. The same clamping rule is used for the month portion of a date difference so the two features agree.
Business days skip weekends only
Only Saturday and Sunday are excluded. Public holidays change every year and are not applied, so the result can differ from an actual working calendar.
Time zone
Today's date follows the device time zone. Away from Korea it can be a day off, so set the reference date explicitly when that matters.
Public holidays are not applied
Business-day math excludes Saturday and Sunday only. Lunar holidays move every year and substitute-holiday rules change, so they are not applied automatically. Cross-check against the official calendar when fixing a deadline.
Exceptions to the age rule
Since June 2023 Korean law and contracts use international age. Conscription and youth-protection law still use year age, which is why some age thresholds change at the start of the year rather than on a birthday.
Do not derive age from national ID numbers
The leading digits alone cannot distinguish a 1900s from a 2000s birth year, and the digit that resolves it is part of sensitive personal data. If you need an age, collect a birth date instead — safer and legally simpler.
