Common year

A **common year** is a calendar year with 365 days.  It is a year that is not a leap year. This means a common year has 52 weeks and one day.  So if a certain year started on a Monday, the following year will start on a Tuesday. Stated differently, a common year always begins and ends on the same day of the week (for example, in 2026, January 1 and December 31 fall on a Thursday). In common years, February has exactly four weeks, so March begins on the same day of the week. November also begins on this day. For example, if February 2026 begins on a Sunday, then March would also begin on a Sunday. November follows the same characteristic.

In a common year, the corresponding months are January and October, February, March, and November, April and July and September and December. No month corresponds to May, June or August.

In the Gregorian calendar, 303 out of every 400 years are common years. In the Julian calendar, 300 out of every 400 years were common years. All the other years are special and known as leap years.

## Years

- 2000, a century leap year, began on a Saturday.
- 2001 began on a Monday.
- 2002 began on a Tuesday.
- 2003 began on a Wednesday.
- 2004, a leap year, began on a Thursday.
- 2005 began on a Saturday.
- 2006 began on a Sunday.
- 2007 began on a Monday.
- 2008, a leap year, began on a Tuesday.
- 2009 began on a Thursday.
- 2010 began on a Friday.
- 2011 began on a Saturday.
- 2012, a leap year, began on a Sunday.
- 2013 began on a Tuesday.
- 2014 began on a Wednesday.
- 2015 began on a Thursday.
- 2016, a leap year, began on a Friday.
- 2017 began on a Sunday.
- 2018 began on a Monday.
- 2019 began on a Tuesday.
- 2020, a leap year, began on a Wednesday.
- 2021 began on a Friday.
- 2022 began on a Saturday.
- 2023 began on a Sunday.
- 2024, a leap year, began on a Monday.
- 2025, began on a Wednesday.
- 2026, began on a Thursday.
- 2027 will begin on a Friday.
- 2028, a leap year, will begin on a Saturday.
- 2029 will begin on a Monday.
- 2030 will begin on a Tuesday.

## Months

These are the 12 months in a year.

- January has 31 days.
- February has 28 days.
- March has 31 days.
- April has 30 days.
- May has 31 days.
- June has 30 days.
- July has 31 days.
- August has 31 days.
- September has 30 days.
- October has 31 days.
- November has 30 days.
- December has 31 days.

There are 7 months with 31 days. There are 4 months with 30 days. There is 1 month with 28 days. In the Julian calendar, introduced by Julius Caesar in 45 BC, every 4 years there are 29 days in February, which is called a leap year. This happens because every year is 365 and 1/4 days but instead of us having a spare quarter of a day in each year we add them all up every 4 years and make an extra day to avoid confusion and make things easier for everyone.
In the Gregorian Calendar, which was introduced in 1582 by Pope Gregory XIII, because the Julian calendar added slightly too many years, three leap years were removed for every 400 years. These are those that are multiples of 100, but not multiples of 400. Thus, in the Gregorian calendar, 2020 is a leap year, but not 2019 and 2021, 1900 is not a leap year even though 1904 and 1896 are, and 2000 is a leap year even though 1900 and 2100 are not.