One moment, the same for everyone
When you set a date and time, the countdown fixes that moment in your time zone and writes the time zone into the share link. A friend who opens the link in New York, Berlin or Tokyo counts down to exactly the same second, and sees under the countdown what time it will be for them.
The time zone rules come from the database built into your browser, daylight saving time included. If a clock change falls between now and your event, the countdown still ends at the right moment. The hours shown are real hours: a night when the clocks change has 23 or 25 of them.
What people count down to
Weddings, holidays, birthdays, exams, retirement, the release of a game or a film, the start of a new job, a baby's due date. For an online launch or a live stream, pick the organiser's time zone, for example 10:00 in Los Angeles, so that every viewer counts to the same second no matter where they live.
Full screen mode turns the page into a large display for a party, a shop window or a classroom, and keeps the screen on while it is shown.
Full days and days on the calendar
The large numbers show complete days plus the remaining hours, minutes and seconds. Below them you also see the days on the calendar, which is how most people count: at 3 pm on 27 October, Christmas is 58 full days and 9 hours away, but 59 days on the calendar. The total hours, total minutes and weeks are shown too.
Nothing is uploaded
The countdown runs in your browser. The share link keeps the settings after the # sign, a part of the address that browsers never send to a server, and your last countdown is remembered only on your own device.