Date Calculator

Give this page two dates and it reports the span between them as a total number of days, as whole weeks plus leftover days, as years, months and days, and as a count of weekdays against weekend days. It also names the day of the week each endpoint falls on. The method is the day-number technique the U.S. Naval Observatory describes for Julian dates: convert each calendar date into a running count of days from a fixed origin, then subtract one count from the other. That single subtraction is immune to unequal month lengths and to leap years, because both are already baked into the count before you subtract. The leap rule itself is the Gregorian one the Naval Observatory states - divisible by four, except centuries, unless divisible by four hundred - so 2000 was a leap year and 1900 was not. The question the tool insists you answer is whether the end date is included. This is not a formatting toggle; it changes the answer by one and it has real consequences. Ask how many days from Monday to Tuesday and there are two defensible answers. One, if you mean elapsed time - that is what subtraction gives, and it is how a hotel bills nights or a bank counts interest days. Two, if you mean how many days you are counting, which is how a jury summons, a project schedule or a "your report is due within 10 days" clause is usually read. The default here is elapsed, and switching the include-end option to yes adds the end date to the count. Legal and contract deadlines are especially prone to this: an off-by-one born of the wrong convention is the most common date error there is, and no amount of careful arithmetic protects you if the convention is wrong. The weekday count follows the same convention. Business days are Monday through Friday, matching the basic federal workweek defined in 5 CFR 610.111. When you include the end date, the start date is included too, so the weekday figure is anchored one day earlier rather than patched with a correction term that would need to know whether the start happened to be a Saturday. What the business-day count deliberately does not do is exclude public holidays, and that omission is a choice rather than an oversight. No single holiday calendar is right for everyone: federal holidays differ from state ones, observed dates shift when a holiday lands on a weekend, and none of it transfers outside the United States. Counting weekdays and saying so plainly is more honest than quietly applying one country's table and being wrong everywhere else. Subtract your own holidays from the weekday figure. Dates entered in the wrong order are reordered rather than rejected, with the reversal flagged, because a negative number or a validation error helps nobody. Inputs are accepted between 1600-01-01 and 2400-12-31. The lower bound exists because the Gregorian calendar is proleptic before the 1582 reform - projecting it backwards is arithmetically exact but historically misleading, since those dates were actually recorded in the Julian calendar. A well-formed string is also checked against the real calendar, so 2023-02-30 is refused rather than silently accepted. Both endpoints are explicit inputs and no system clock is consulted anywhere, which is why a result link means the same thing next year as it does today. If what you want is somebody's age rather than a raw span, the age calculator applies the calendar-month rules that make birthdays work properly, and the percentage calculator is handy for turning elapsed days into a share of a project timeline.