About this page
Three sums the calendar keeps asking for: the days between two dates—also spelled out as weeks, as calendar months, and, for the long spans, as years; the weekday any date falls on, with its ISO week number; and where today stands in the year. Everything is worked out in your browser from the calendar itself, with leap years counted properly and no off-by-one surprises from daylight saving.
Questions
How many days are there between two dates?
Pick both dates and the page counts the days between them instantly, in either order, and restates the same span as weeks and days, as calendar months and days, and—once it runs past a year—as years, months and days. Everything is computed from the calendar itself.
How many years is that?
Any span of a year or more is also given in whole years, then the leftover months and days: 16,000 days from 1981 comes out as 43 years and change, not a division by 365. The years are counted on the calendar, so leap days are already inside them—a birthday on 1 March is a year older on 1 March, whether or not February had 29 days.
Are both endpoint days included in the count?
The result is the difference between the two dates: Monday to Friday of the same week is 4 days. Some counts—days of an event, nights of a stay—want both endpoints included; if that is what you mean, add 1 to the number shown.
What is an ISO week number?
The week’s position in the year under ISO 8601, the convention planners and payrolls use: weeks run Monday to Sunday, and week 1 is the week containing the year’s first Thursday. A year has 52 or 53 such weeks.
Does it handle leap years?
Yes. The counting works on the real calendar, so 29 February is a day like any other when it exists, the day-of-year runs to 366 in leap years, and spans across leap days come out exact.
More instruments: the turn of the seasons, the phase of the moon and a fullscreen clock with pomodoro—or see all of them. Or search the site.