About What’s the Date Today
One question, answered properly: what is the date today, where you are? Plus the handful of date and time tools that people need right after it.
What’s the Date Today is an independent reference site. It carries no advertising, and it counts visits in aggregate without cookies. Each page answers one question in full, shows the answer first, and explains how the answer was reached, with links to the official sources behind every rule.
What is on the site
- Today’s date: the date and day where you are, in every format.
- What time is it: exact time, UTC offset and daylight saving time.
- Days from today: count days, weeks or months forward or back.
- Days between dates: days, weeks, months and business days.
- Day of the week: the weekday of any date, and how to work it out.
- Week number: ISO 8601 and US week numbers for any year.
- Calendar: printable year calendar with week numbers.
- Julian date: day of the year, YYDDD codes and Julian Day.
- Time zone converter: convert a time between any two zones.
- Leap year: the leap year rule, next leap year, leap seconds.
- Date formats: how to write the date, by country and use.
How the date and time are worked out
The date depends on where you are, so the site never shows one fixed date to everyone. When you request a page, our server reads the approximate time zone that our hosting network derives from your connection and writes today’s date, day and time for that zone into the page before sending it, so the answer is there the moment the page appears. If no time zone is available, the server uses New York time.
Your browser then takes over. It reads your device’s time zone setting, which wins over the network guess, recalculates every value, keeps the clock running, and changes the date at your local midnight without a reload. It also asks our server for the exact time and compares it with your device clock. If they differ by more than two seconds, the page tells you and corrects the times it shows. Our server’s clock is synchronized with internet time servers using the Network Time Protocol.
Time zone rules come from the IANA Time Zone Database built into your browser and into our server. Calendar calculations count whole days through the Julian Day Number, the continuous day count used by astronomers, with the conversion formulas published by the U.S. Naval Observatory. Weeks follow ISO 8601, and US week numbers follow the Sunday-start system Microsoft documents for Excel. US federal holidays are computed from the law, 5 U.S.C. 6103, with the weekend observance rules published by the Office of Personnel Management. Other calendars (Hebrew, Islamic, Chinese, Persian, Indian and Japanese) come from the Unicode CLDR data in your browser.
How results are checked
Every calculation on the site is covered by automated tests that compare it with independent published values, including:
- the weekdays of dates fixed by the sources, such as Thursday, October 4, 1582 and Friday, October 15, 1582 (USNO), and Wednesday, September 2 and Thursday, September 14, 1752 (Calendar Act 1750);
- ISO week numbers, including the examples in the POSIX standard and in Microsoft’s ISOWEEKNUM and WEEKNUM documentation, and every year with 53 weeks from 2000 to 2040;
- the US federal holiday schedules published by OPM for every year from 2021 to 2030, including New Year’s Day observed on December 31 of the year before;
- Julian Day 2451545.0 at noon on January 1, 2000, the J2000.0 epoch defined by the USNO;
- month-end arithmetic such as January 31 plus one month, leap days, and Microsoft’s NETWORKDAYS example;
- daylight saving change days, including times that are skipped or happen twice, and two visitors on either side of midnight receiving two different dates.
Keeping it current
Nothing on the site needs a daily update: every value that depends on today is computed when you load the page. What changes over time are the rules. Time zone rules change when governments change them, and arrive with updates to the IANA database in browsers and in our server. We check the OPM holiday schedule when it publishes each new year, the IERS Bulletin C on leap seconds every six months, and the law for changes to federal holidays or daylight saving time, and we update the pages and their tests when a rule changes.
Sources
- U.S. Naval Observatory: calendars, the Gregorian leap year rule and Julian dates
- NIST: internet time service, UTC(NIST), daylight saving time and leap seconds
- IANA Time Zone Database: time zones and their history
- IERS Bulletin C and CGPM 2022 Resolution 4: leap seconds
- 5 U.S.C. 6103, OPM federal holidays and 15 U.S.C. 260a: holidays and daylight saving time
- Calendar (New Style) Act 1750: the 1752 change in Britain and its colonies
- POSIX strftime, RFC 3339, RFC 5905 and Microsoft’s Excel documentation: formats, week numbers and formulas
- GPO Style Manual, the GOV.UK style guide, the W3C and Unicode CLDR: how dates are written
Corrections
If a date, a time or a result looks wrong, tell us what you saw, where you are and what you expected. We check every report, fix the page or its test when we are wrong, and reply with what we found. See the contact page.
The company that publishes What’s the Date Today is identified in our privacy policy. You can reach us at [email protected].