Date & Time Calculators

To see age, star sign, zodiac and birthstone all from one birth date, use the age calculator; for how long is left until a fixed date like a wedding or exam, use the D-day calculator. If you only need the exact number of days between two dates, the date difference calculator is simpler.

The lunar-solar converter handles leap months from 1900 through 2100, so it's useful for turning a lunar-calendar date — an ancestral rite or birthday — into the matching solar date each year, and the 49-day memorial calculator computes the traditional Buddhist memorial date from a date of passing.

The couple D-day calculator flags milestones like the 100th, 200th day and first anniversary from the day you started dating, and the business-days calculator counts only actual working days excluding public holidays — handy for scheduling a project. The military discharge calculator works out the discharge date and promotion dates from an enlistment date.

A one-day discrepancy usually traces to whether the first day counts. Korean civil law starts a period on the following day, while anniversaries and age are conventionally counted from the first day — leaving the same dates to produce different answers unless the basis is fixed.

Deadlines need calendar days kept apart from business days, which exclude weekends and public holidays: the same ten days can run two real weeks. Korean holidays shift year to year with substitute designations, so long schedules need the relevant year's calendar.

Lunar dates land on a different solar date each year because twelve lunar months fall some eleven days short of a solar year, corrected by inserting a leap month every few years. Seollal, Chuseok and Buddha's Birthday move for this reason.

Age was unified to international reckoning for administrative and contractual purposes in June 2023, though military service and youth protection still use calendar-year age — worth checking which basis a given form means.

Time zone arithmetic has to account for daylight saving, which differs by country and period and runs on the opposite schedule in the southern hemisphere. Scheduling across regions means checking whether the other side is currently observing it.

Working-day and service-period counts feed into pay, leave and severance. How the start and end dates are counted can differ by a day, and that day can shift which leave entitlement or severance band applies.

A countdown puts the target itself at D-day and the day before at D-1. Counting elapsed time conventionally makes the start day one, so the hundredth day falls 99 days later — and because apps default differently, the same date often reads a day apart.

International and traditional Korean age can differ by up to two years, since a December birth reaches two in traditional reckoning within a month. The gap is one year before the birthday and two after.

Leap years fall on years divisible by four, except centuries not divisible by 400. A 29 February birth has no counterpart in common years, and age is treated as advancing once 28 February passes.

Ancestral rites are often kept on lunar dates, so their solar date moves each year. A date falling in a leap month has no counterpart in ordinary years and is customarily observed in the ordinary month of the same number.