Today's Date and Time

Because that is how long Earth takes to orbit the Sun: 365.2422 daysto be precise. The Gregorian calendar handles the leftover quarter-day with a leap-year rule — add a day every 4 yearsskip every 100but keep every 400. That gives an average year of 365.2425 dayswhich only drifts by one day every 3,236 years. So 2000 was a leap yearbut 1900 and 2100 are not.

In theorydividing 360° of longitude by 24 hours gives a 15°-wide zone for each hour. In practicetime zones follow politicsnot geometry. China spans roughly 5 geographic zones but uses a single time (UTC+8) imposed by Beijing. India uses UTC+5:30Nepal uses UTC+5:45and the Chatham Islands use UTC+12:45. Including these half- and quarter-hour offsetsthere are about 38 distinct standard offsets in use today.

UTC (Coordinated Universal Time) is the global referencedefined by an ensemble of about 450 atomic clocks at roughly 80 laboratories worldwide and coordinated by the BIPM in France. GMT (Greenwich Mean Time) is the historical British time zone based on the Sun crossing the meridian at the Royal Observatory in Greenwich. They agree to within a fraction of a secondbut UTC is the modernatomic-based standard. Your local time is simply UTC plus or minus your country's offsetpossibly with daylight saving applied.

A Unix timestamp is the number of seconds that have elapsed since January 11970 at 00:00:00 UTC — a moment called "the Unix epoch." Because it is just an integerit is timezone-independentsorts naturallyand avoids the ambiguity of human-readable dates. Almost every databaselog fileand API uses it under the hood. The 32-bit version of this counter will overflow on January 192038 (the "Y2038 problem")which is why modern systems store it as a 64-bit integer.

Daylight saving time (DST) shifts clocks one hour forward in spring and back in autumn so that more daylight falls in the evening hours during summer. It was first proposed by the New Zealand entomologist George Hudson in 1895 and first adopted nationally by the German Empire in April 1916 to save coal during the First World War. Today about 70 countries observe DSTmostly in Europe and North America. Its actual energy savings are small and disputedand several jurisdictions are working to abolish it.

The seven-day week is one of the oldest continuously used units of timedating back at least 4,000 years to the Babylonianswho linked each day to one of the seven celestial bodies visible to the naked eye: the SunMoonMarsMercuryJupiterVenusand Saturn. The Romans inherited itChristianity carried it across Europeand Islam carried it across the Middle East and North Africa. Unlike the year and the monththe seven-day week has no astronomical basis — it just turned out to be too useful and too embedded in religious practice for any reform attempt to dislodge it.

The time displayed is your computer's clockwhich on a modern machine is synchronized to within tens of milliseconds of UTC over the public internet using the Network Time Protocol (NTP)specified in RFC 5905. NTP servers themselves trace their accuracy back to atomic clocks at national metrology institutes. For everyday purposes — meetingsdeadlinesschedules — that is far more precision than you will ever need.

ISO 8601 is the international standard for writing dates and times. Its core rule is to write the largest unit first: YYYY-MM-DD for datesHH:MM:SS for timesseparated by a "T" for combined timestamps (e.g.2025-01-25T14:30:00Z). The format is unambiguous across cultures (03/04/05 means three different things in the USEuropeand Japan)it sorts correctly as a plain stringand it is the format used by virtually every databaselog fileand JSON API in the world.

Atomic clocks measure time by counting the oscillations of atoms — typically cesium-133which vibrates exactly 9,192,631,770 times per second. This frequency is so stable that the best atomic clocks would not gain or lose a second in millions of years. These clocks are maintained by national laboratories worldwide and their outputs are averaged to produce UTC. Your phone and computer synchronize with these clocks through NTP serverswhich is why the time on your screen is accurate to within a few milliseconds of the official global standard.

Yes. All date and time calculations are performed locally in your browser using JavaScript. Once the page has loadedthe tools continue to work even if your internet connection is interrupted. No personal data is sent to any server.

Countries near the equatorsuch as most of AfricaSoutheast Asiaand equatorial South Americasee very little variation in daylight hours throughout the yearso shifting clocks would provide no meaningful benefit. Other countrieslike Russia and Chinahave experimented with DST and abandoned it due to the confusion and economic disruption the clock changes caused. As of 2026about 70 countries still observe DSTbut several — including the European Union and various U.S. states — have ongoing legislative efforts to abolish it permanently.