Event Countdown

This calculator finds the exact number of days -- and, as a derived figure, hours -- between any two Gregorian calendar dates, using a Julian day number conversion so it handles leap years and varying month lengths correctly across any span from a single day to thousands of years. Enter a start date (year, month, day) and a target date in the same format, and the calculator converts each to its Julian day number, subtracts, and reports the absolute difference as Days apart, with Hours simply that figure multiplied by 24. Because the result is an absolute value, the calculator works the same way regardless of which date comes first: if the target date falls before the start date, it flags Target before start? as "Yes" and still reports the full magnitude of the gap rather than a negative number.

This makes it useful for two different jobs -- counting down to a future wedding, deadline, or vacation, and counting up from a past date to see how long ago something happened -- without needing a separate calculator for each direction. Because both dates are entered independently across six separate year/month/day fields, the relationship between any single field and the final day count depends on where the other five fields sit -- raising Start year, for instance, can either raise or lower Days apart depending on which side of the target date it lands on, and even Target day can move Days apart in either direction depending on which month it falls in relative to the start date -- so this calculator's result is best understood by trying your own two dates rather than through a fixed rule of thumb.