Time and date reference
- Days in a year
- 365, or 366 in a leap year
- Weeks in a year
- 52 weeks and 1 day
- Days in a month
- 28 to 31 (table below)
- Seconds in a day
- 86,400
- First day of the week
- Monday (ISO 8601) or Sunday (US)
- Next leap year
- 2028
- Today
- Day 307 of 365, week 45
- This month
- November has 30 days
Days in each month
| Month | Days | Month | Days |
|---|---|---|---|
| 1. January | 31 | 7. July | 31 |
| 2. February | 28 or 29 | 8. August | 31 |
| 3. March | 31 | 9. September | 30 |
| 4. April | 30 | 10. October | 31 |
| 5. May | 31 | 11. November | 30 |
| 6. June | 30 | 12. December | 31 |
Seven months have 31 days, four have 30 and February has 28, or 29 in a leap year. Two old memory aids still work. The rhyme “Thirty days hath September, April, June and November” names the 30-day months. On the knuckles of a fist, every knuckle is a 31-day month and every hollow between them is a shorter month, counting January on the first knuckle and starting again after July, so July and August both land on knuckles. The odd pattern is Roman: the months and their lengths were fixed in the Julian calendar and carried over unchanged into the Gregorian calendar of 1582.
Units of time
| Period | Seconds | Minutes | Hours | Days |
|---|---|---|---|---|
| 1 minute | 60 | 1 | ||
| 1 hour | 3,600 | 60 | 1 | |
| 1 day | 86,400 | 1,440 | 24 | 1 |
| 1 week | 604,800 | 10,080 | 168 | 7 |
| Common year (365 days) | 31,536,000 | 525,600 | 8,760 | 365 |
| Leap year (366 days) | 31,622,400 | 527,040 | 8,784 | 366 |
| Average Gregorian year | 31,556,952 | 525,949.2 | 8,765.82 | 365.2425 |
The average Gregorian year is the 400-year average of 146,097 days, the length the calendar is designed around. The second is the SI second of atomic clocks. A calendar day of 86,400 seconds matches the Earth’s rotation closely enough that only 27 leap seconds were ever added to UTC, the last at the end of 2016; from 20 May 2027 UTC will have none, by decision of the CGPM. Unix time and most computers count every day as exactly 86,400 seconds.
Does the week start on Sunday or Monday?
Both, depending on the country, and a few countries start it on Saturday or Friday. The international standard, ISO 8601, numbers the days of the week from Monday (1) to Sunday (7), and its week numbers count Monday-to-Sunday weeks. Most of Europe, as well as China, Australia and New Zealand, prints calendars that way. The United States, Canada, Mexico, Brazil, Japan, India and many others start the printed week on Sunday. Egypt, Iraq, Iran and other countries whose weekend falls on Friday start it on Saturday.
The data below comes from the Unicode CLDR, the locale database that phones, operating systems and browsers use to lay out calendars. CLDR describes its setting as the first day of the week “in a calendar page view”, a convention and not a law. It is also not always the first working day. In Israel the printed week starts on Sunday, and Sunday is also a working day there, because the weekend is Friday and Saturday.
Countries whose calendars start the week on Sunday
American Samoa, Antigua and Barbuda, Bahamas, Bangladesh, Belize, Bhutan, Botswana, Brazil, Cambodia, Canada, Colombia, Dominica, Dominican Republic, El Salvador, Ethiopia, Guam, Guatemala, Honduras, Hong Kong, Iceland, India, Indonesia, Israel, Jamaica, Japan, Kenya, Laos, Macao, Malta, Marshall Islands, Mexico, Mozambique, Myanmar, Nepal, Nicaragua, Pakistan, Panama, Paraguay, Peru, Philippines, Portugal, Puerto Rico, Samoa, Saudi Arabia, Singapore, South Africa, South Korea, Taiwan, Thailand, Trinidad and Tobago, U.S. Virgin Islands, United States, United States Minor Outlying Islands, Venezuela, Yemen, Zimbabwe.
Countries whose calendars start the week on Saturday
Afghanistan, Algeria, Bahrain, Djibouti, Egypt, Iran, Iraq, Jordan, Kuwait, Libya, Oman, Qatar, Sudan, Syria. In the Maldives the week starts on Friday.
Monday
All other countries in CLDR, including the United Kingdom, Germany, France, Spain, Italy, Russia, China, Australia and New Zealand, start the week on Monday, as does the CLDR world default. Even where Sunday comes first on wall calendars, as in the US, many diaries, timetables and spreadsheets in business use Monday-first weeks.
Why some weeks start on Sunday
The seven-day week reached the modern calendar through Jewish and Christian practice. In that tradition the Sabbath, Saturday, is the seventh day, so Sunday is the first. Several languages still count from Sunday. Portuguese calls Monday segunda-feira, the second day, and Hebrew calls Sunday yom rishon, the first day. As Sunday became the day of rest in Christian countries, the working week came to begin on Monday. Standards bodies chose that order, and ISO 8601 made Monday day 1.
Weekends that are not Saturday and Sunday
Most countries have a Saturday–Sunday weekend, but CLDR records these exceptions:
- Friday and Saturday: Algeria, Bahrain, Egypt, Iraq, Israel, Jordan, Kuwait, Libya, Oman, Qatar, Saudi Arabia, Sudan, Syria, Yemen
- Thursday and Friday: Afghanistan
- Friday only: Iran
- Sunday only: India, Uganda
Weekends also change by law from time to time, and CLDR follows with a delay. For payroll or deadlines in another country, check its official calendar.
Weekdays (Monday to Friday) in each month
Business days before public holidays: these counts depend only on the calendar, so they hold in every country with a Saturday–Sunday weekend. Subtract the public holidays that fall on weekdays in your country or region.
| Month | 2026 | 2027 | 2028 |
|---|---|---|---|
| January | 22 | 21 | 21 |
| February | 20 | 20 | 21 |
| March | 22 | 23 | 23 |
| April | 22 | 22 | 20 |
| May | 21 | 21 | 23 |
| June | 22 | 22 | 22 |
| July | 23 | 22 | 21 |
| August | 21 | 22 | 23 |
| September | 22 | 22 | 21 |
| October | 22 | 21 | 22 |
| November | 21 | 22 | 22 |
| December | 23 | 23 | 21 |
| Year | 261 | 261 | 260 |
A month has between 20 and 23 weekdays. February in a common year always has exactly 20, because it is exactly four weeks. A 31-day month has 23 when it starts on a Monday, Tuesday or Wednesday, since those three weekdays then occur five times. Weeks in a year explains why a year has 260, 261 or 262.
Explainers on this site
- Weeks in a year
- 52 weeks and 1 day, the years with 53 ISO weeks, workdays and pay periods.
- Leap years
- The next February 29, a checker for any year, and why 1900 and 2100 are not leap years.
- The Gregorian calendar
- The 1582 reform, the missing days, when each country switched, Julian dates converted.
- Date formats and ISO 8601
- Today in every format, which countries write which order, and format codes in software.
- Week numbers
- This week’s ISO and US week numbers and how they differ at the turn of the year.
- Day of the year
- Today’s day number and the ordinal date.
- Julian date
- The two meanings: day-of-year codes such as 26306, and the astronomers’ Julian Day.
- Unix time
- Seconds since 1970, milliseconds, and the year 2038 limit.
- Military time
- The 24-hour clock written as four digits, with a chart.
- AM and PM
- What the abbreviations mean, and noon and midnight.
- Daylight saving time
- The next clock change and the rules in the US, Europe and elsewhere.
- Time zones
- Every zone abbreviation, UTC offset and IANA zone.
- Islamic (Hijri) date
- Today in the Umm al-Qura calendar and why local dates can differ.
- The exact time
- A clock synchronised to our server, and how its accuracy is measured.
- How we keep time
- Clock sync, time zone data and the calendar arithmetic behind every page.