Pick a date and time, or tap a holiday from the list, and watch the days, hours, minutes and seconds fall away. When it reaches zero the page says so properly — confetti, a chime and the moment marked. Everything runs in your browser, and the countdown you set is kept in the address bar, so you can bookmark it or send the link to someone.
Counted in the time zone your device is set to.
A countdown is a simple thing to build and an easy one to get quietly wrong. These are the four decisions behind this one.
A countdown that reaches zero and shows four zeros has failed at the one job it had. At zero the panel turns over, confetti falls, a chime plays and the clock carries on the other way, so the moment is still readable an hour later. Open the page on the morning of the day and you still get the celebration — you are not late, you are on time.
Every tick works out the answer again from your device's clock rather than adding a second to the last one. That matters because a browser slows a background tab down to about one tick a minute: a counter that adds up its own seconds would be badly wrong by morning, and this one is exact the moment you look at it.
The countdown you set is written into the address bar, not into your device and not onto a server. Bookmark it, or send the link to whoever else is waiting, and it opens on the same date with the same name. Close the tab and nothing of it is left behind.
Visak Bochea, the Royal Ploughing Ceremony, Pchum Ben and the Water Festival follow the Khmer lunar calendar, and their Gregorian dates are fixed each year by sub-decree. They are named in the list rather than counted down to until that year's sub-decree has been entered. Chinese New Year is a table of published dates for the same reason — when the table runs out the event stops being offered instead of being guessed at.
Watching the number fall is the easy part. We build revision timetables backwards from the date that matters — tell us when the paper is and we will tell you what each week needs to cover.