Date Tools

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Twenty-five calculators for a calendar and a clock

Working days between two dates with a country's holidays taken out, a deadline in working or calendar days, the ISO week for a date and the seven dates of a week, the leap-year rule spelled out, Easter and the twelve feasts that hang off it in both churches, a year of public holidays with the long weekends marked, and the three different things that are all called a Julian date.

Then the clock: how long between two times of day when the span crosses midnight, a column of durations added up with a running total, the twelve- and twenty-four-hour clocks with the whole chart, timesheet rounding that says which way the total drifted, and lap times split apart and put back together.

There is no calendar dependency behind any of this. The conversions, the anonymous computus, the ISO week rule and the date parser are two hundred lines in a shared crate, and every one of them is pinned in its tests to published dates rather than to what the code happened to produce. Everything runs inside this browser tab, compiled to WebAssembly.

Between two dates

Business days
Working days between two dates, weekends and holidays taken out.

Deadline
Where a period of working or calendar days lands.

Working hours
Hours between two dates at a stated working day, break taken out.

The calendar

Week number
The ISO week for a date, or the seven dates of a week.

Leap year
Whether a year is one, and the century rule that decides it.

Easter date
Easter Sunday and the twelve feasts that hang off it, in both churches.

Public holidays
A year of holidays for seven countries, with the long weekends marked.

Julian date
The three different things called a Julian date, side by side.

Clock and stopwatch

Add up times
A column of durations added or subtracted, with the running total.

24-hour clock
Between the twelve- and twenty-four-hour clocks, with the whole chart.

Lap times
Laps, splits, the fastest and the slowest, and the pace with them.

A run of dates

Date sequence
A column of dates at a chosen step, skipping what should be skipped.

Shift rota
A rota from a pattern that repeats, with each person's tally.

One date

Countdown
How long until a date, in every unit somebody counts it in.

Moon phase
The phase and how much is lit, from a mean lunation that says its error.

Zodiac sign
The western sign and the Chinese animal, with both boundaries stated.

Pet age
A dog's or a cat's age by a published curve, not by seven.

Converting

Date formats
A column of dates in one shape, and a warning when the column disagrees with itself.

Meeting planner
The hours several places share, from offsets you give. No time-zone database.

Questions

How many working days are there between two dates?
That depends on two things a bare subtraction does not know: which days you count as a working week, and whose public holidays to take out. Both are settings here, and the holidays are rules rather than a table of dates, so they work for any year. The default takes no country's holidays out at all, because doing that silently would give a different answer with nothing said.
Why does my spreadsheet say a night shift is minus sixteen hours?
Because 22:45 to 06:30 crosses midnight, and subtraction does not know that. A time of day has a ceiling and wraps; a duration does not. The tools here read the two with two different parsers, and every one of them says which of the two it is holding.
Which week number is 1 January in?
In 2021 it was week 53 of 2020, and 31 December 2019 was week 1 of 2020. An ISO week belongs to the year containing its Thursday, so a week number without its year is half an answer — and the tool says so on exactly the dates where it matters.
Is anything I type uploaded?
No. The tools are compiled to WebAssembly and run inside the browser tab. Nothing you type is sent to a server, and you can watch your browser's network panel while you use one to see that nothing leaves the page.