Setting up a countdown: date, time, title and time zone
Choose a date, a time (midnight if you leave it) and an optional title of up to 60 characters, then press Create. The big display shows days, hours, minutes and seconds left; below it is the exact target written out, for example "Friday, 1 January 2027, 00:00 KST (UTC+09:00)", so there is never any doubt which moment you are counting to.
The time zone defaults to the one your device is in. Change it only when the event happens somewhere else: a launch in Florida, a match in London, a release that goes live at midnight Pacific. The countdown then targets that zone's wall-clock time, and the display adds a second line with the same moment in your own time.
Dates from 1900 up to 100 years ahead are accepted, and the form checks the calendar: 29 February is allowed only in a leap year, and 31 April does not exist. Below the form, four event chips open ready-made countdowns to New Year, Christmas, Halloween and Valentine's Day.
How the days, hours and minutes are calculated
The display is the exact difference between the target moment and now, split into days of 24 hours, then hours, minutes and seconds, and it refreshes every second. Because the split is done on real elapsed time, a daylight-saving change in between shows up as an odd hour: from 1 October to Christmas in London is 85 calendar days but 85 days and 1 hour of real time, because the clocks go back in late October. The number of days is therefore a true count of 24-hour periods, which is what "days left" usually means and what timeanddate.com shows as well.
A line underneath gives the same span in other units: weeks and days, total hours, total minutes and total seconds. Seconds are rounded up while counting down, so the display reaches 00:00:00 only at the exact moment, never a second early.
Sharing a countdown: the link carries the moment, not just the date
Share link copies an address such as ?t=2027-01-01T00:00:00+09:00&n=New+Year. The time is written with its UTC offset, so a friend in New York who opens it sees the identical moment converted to their clock (10:00 on 31 December) and a note that the original is KST. Without the offset, a shared "1 January 00:00" would be ambiguous by up to 26 hours.
If you chose a named time zone, the link also carries it, so the display can say "KST" rather than just "UTC+09:00". The title is in the link too, and nothing is stored on a server: the address is the whole countdown, so bookmarking it brings it back on any device.
Reaching zero: alarm, message and elapsed time
If the page is open when the moment arrives, the chosen alarm sound plays and repeats until you press Stop alarm, Space or Esc, the title shows your event name with a celebration, and a counter starts showing how long ago it happened. A desktop notification appears when the tab is in the background and notifications are allowed.
The sound is pre-scheduled on the browser's audio clock during the last 100 hours before the target, the same mechanism the timer uses, so a background tab on a computer rings on time. Keep the tab in front on an iPhone, since Safari pauses hidden pages. A link you open after the moment has already passed does not ring; it simply shows the time elapsed.
Past dates: counting the days since
Enter a date in the past and the display counts upward instead: days, hours, minutes and seconds since that moment, for a quit date, a baby's age in days, days since the last incident or how long a project has run. The same link format works, and the tab title shows the elapsed days.
For anniversaries you usually want the next occurrence, not the time since the last one; set next year's date for that, or use the event pages, which roll over to the following year by themselves.
Event countdowns: New Year, Christmas, Halloween, Valentine's Day
Each event page targets midnight at the start of the day in your own time zone, the usual convention for "days until Christmas". After the day has passed, the page automatically counts to next year's date; on the day itself it shows a greeting and how long ago midnight was. Nothing needs to be typed, so the pages are good to bookmark or put on a classroom screen.
Christmas is 25 December in the Western calendar; Orthodox churches that follow the Julian calendar celebrate on 7 January, for which you can set a custom countdown here. New Year is the only one of the four where the moment itself, midnight, is the celebration; for the others the countdown ends when the day begins.
Countdown, timer or stopwatch?
Use this countdown for a moment on the calendar: an exam, a flight, a product launch, a holiday. Use the timer for a length of time starting now, such as 10 minutes for tea or 45 minutes for a lesson, which rings when it reaches zero. Use the stopwatch to measure how long something takes, with laps.
The Pomodoro timer and the interval timer run repeating focus-and-break or work-and-rest periods. All five tools share the same alarm sounds and settings, and all of them keep exact time from the clock rather than from screen updates.