New Year Countdown 2027

Formulas

• The visitor's calendar date comes from the clock in their own IANA time zone. The target is the next 1 January or 25 December after that date; on the day itself the page shows the greeting and counts to the following year.

• Days until is the difference between the two calendar dates, counted with a day-number formula for the Gregorian calendar rather than by subtracting clock times, so daylight-saving changes and leap days cannot skew it.

  days = dayNumber(target) − dayNumber(today)

• The clock splits the real time left, from now to the first instant of the target date in the visitor's zone, into days of 24 hours, hours, minutes and seconds. That can read one day lower than the calendar count until midnight, because the calendar counts today as a day.

  remaining = midnight(target) − now

• Weeks and days divide the calendar count by 7. Sleeps are the nights before the holiday morning, which equals the calendar count.

  weeks = ⌊days ÷ 7⌋, rest = days mod 7, sleeps = days

• Weekdays counts Monday to Friday from today (included) up to the day before the holiday. Public holidays are not removed.

Sources

• IANA, Time Zone Database. The database of local-time history, including daylight-saving changes, that browsers use to turn an instant into a wall-clock time in a zone.
• MDN Web Docs, Intl.DateTimeFormat.prototype.resolvedOptions(). How the page learns your IANA time zone name: it is the runtime's default time zone.
• US Office of Personnel Management, Federal holidays. Lists New Year's Day (January 1) and Christmas Day (December 25), and shows that weekend holidays are usually observed on the nearest weekday, which the weekday count does not model.

How we test this

This tool is checked against independent formulas every time the site is released, and a release does not ship if a check fails. Example from the test suite: 31 December 2026, 11:30 pm UTC gives 1 day on the calendar, 30 minutes on the clock. The test checks the calendar day count, the year the page names (2027) and the thirty minutes left.

The test is “New Year: Dec 31 counts down to the new year, Jan 1 is the holiday, Jan 2 counts to the year after” in tests/countdown.test.mjs. More on how all tools are tested: our testing approach.

Assumptions and limits

• It trusts your device's clock and time zone setting. If either is wrong, so is the countdown.
• Midnight is local: people further east reach the new year earlier, so the countdown shows the moment in your own zone, not a global one.
• The weekday count does not exclude public holidays or the days your workplace or school is closed.
• The calendar is the Gregorian one. Other new-year dates (Lunar New Year, Rosh Hashanah, Nowruz) are not modeled.