# Days in a year

There are 365 days in a year in a common year of the Gregorian calendar and 366 days in a leap year. Leap years occur every four years. The average number of days in a year is 365.2425 days.

## How many days in a year

The number of days in a year is an approximation of the period of time it takes the Earth to orbit the sun. On average, for the Gregorian calendar, the average length of the calendar year is 365.2425 days. Over the course of a complete leap cycle (400 years in the Gregorian calendar), there are 97 leap years and 303 common years.

### Work days in a year

In the US, there are approximately 260 work days in a common year. This counts federal holidays as work days. Excluding federal holidays, there are approximately 249 work days in a common year in the US.

### Weekend days in a year

There are an average of 104 weekend days in a year.

### Federal holidays in a year

In the US, there are 11 federal holidays a year. In years when there is a presidential election, parts of the country also get Inauguration Day as a federal holiday. Federal holidays in the US either fall on the same date every year or on the same day of the week every year. Refer to the following US federal holiday table:

Federal holiday | Date/week |
---|---|

New Year's Day | January 1 |

Inauguration Day* | January 20 (or 21 if 20 is a Sunday) |

Martin Luther King, Jr. Day | 3rd Monday in January |

George Washington's Birthday | 3rd Monday in February |

Memorial Day | Last Monday in May |

Juneteenth | June 19 |

Independence Day | July 4 |

Labor Day | First Monday in September |

Columbus Day | Second Monday in October |

Veterans Day | November 11 |

Thanksgiving Day | 4th Thursday in November |

Christmas Day | December 25 |

*Note that Inauguration day only happens every 4 years when there is a presidential election, and for the most part only those working in Washington DC may observe this holiday.

### School days in a year

In the US, there are 180 school days in a year in most states. This does vary by state, but typically the range is between 160-180 school days per year. Some states such as Kansas (186), Illinois (185), and North Carolina (185) have a larger number of required school days per year. Others do not have a stated number of school days per year.

## What is a day

A day is defined as the approximate period of time taken for the Earth to fully rotate once around its axis, or 24 hours on average. These 24 hours are broken up into morning, noon, afternoon, evening, and night. This cycle repeats every day for the course of the year, but depending on the time of the year, the length of each part of the day changes. For example, there are more daylight hours in a given day during summer than winter. Also, depending on the location on Earth, there may be more or fewer daylight hours. For example, in some parts of the Arctic, the sun may never set at certain times of the year.

### Calendar day

A calendar day, also referred to as a civil day, most commonly starts at midnight. It is divided into 24 hours, each of which has 60 minutes, with each minute comprised of 60 seconds. This is the day used in the Gregorian calendar. When measuring time, a common clock time is defined for an entire region. This time is based on the local mean solar time at a given central meridian. These regions are referred to as time zones, and there are 40 zones used throughout the world. These zones are all defined with reference to the central zone which uses Coordinated Universal Time (UTC). This central zone is referenced as UTC+00, and each region is some offset of UTC+00 denoted by stating the number of hours offset (either +/-) from UTC+00. For example, UTC+06 indicates adding 6 hours to UTC+00.

### Solar day

A solar day is the time it takes for the Sun to reach its highest point in the sky. On average, the length of a solar day is 86,400.002 seconds, though it can be up to 7.9 seconds longer or shorter than 86,400 seconds (24 hrs).

### Sidereal day

A sidereal day is the time it takes the Earth to make one entire rotation with respect to a fixed distant object such as a star. On average, a sidereal day is 4 minutes less than a solar day and lasts approximately 23 hours, 56 minutes, and 4.09 seconds. There are approximately 366.2422 sidereal days in one mean tropical year, as compared to 365.2421875 solar days.

## What is a year

A year is the orbital period of a planetary body. Most commonly, when we talk about a year, we are talking about Earth's orbit around the Sun. On Earth, a year is marked by the passing of seasons due to the axial tilt of the Earth, which includes changes in the weather, the hours of daylight, vegetation, and soil fertility.

### Calendar year

A calendar year begins on the first day of the New Year and ends on the day before the following New Year's Day. In the Gregorian calendar, the calendar year begins on January 1st and ends on December 31st. A calendar year has a whole number of days. In the Gregorian calendar, there are 365 days, but to account for the difference with respect to the solar year (tropical year), one day is added every 4th year. This day is called a leap day, and a leap year is a year with 366 days.

#### Common year

A common year in the Gregorian calendar is a calendar year with 365 days. A common year is the typical year in a calendar. It is contrasted with a leap year. Both calendar years and leap years are necessary to keep the calendar aligned with the solar year (tropical year).

#### Leap year

A leap year is a calendar year that has an extra day. In the Gregorian calendar, a leap year has 366 days rather than 365 days.

Leap years exist to keep calendars synchronized with whatever event they track. A year is the amount of time it takes the Earth to orbit the sun, but this number is not a whole number, so a day needs to be added periodically. A year is 365.2425 days in the Gregorian calendar, so every 4 years, one day is added to keep the calendar and the actual orbit in sync.

The extra day is added on February 29^{th} of every year that is an integer multiple of 4 that is not evenly divisible by 100. Years that are evenly divisible by 100, except those that are also evenly divisible by 400, are not leap years. For example, 2023 is not a leap year since it is not an integer multiple of 4. 2024 is a leap year since it is an integer multiple of 4 and it not evenly divisible by 100. 2100 is not a leap year since it is evenly divisible by 100 but not evenly divisible by 400. 2000 is a leap year since it is evenly divisible by 100 and is also evenly divisible by 400.

### Solar year

A solar year, also referred to as a tropical year, is the time it takes the Sun to return to the same position in the sky of a celestial body, such as the Earth, thus completing a full cycle of seasons. This is the type of year used in tropical solar calendars such as the Gregorian calendar.

### Sidereal year

A sidereal year is the time that it takes the Earth to orbit the Sun with respect to the fixed stars. A sidereal year is approximately 20 minutes and 24.5 seconds longer than the mean tropical year.

## Gregorian calendar

The Gregorian calendar is the most widely used calendar in the world. It is a solar calendar with 12 months, each of which has 28-31 days. In a common year in the Gregorian calendar, there are 365 days; in a leap year, there are 366 days. The number of days in each month of the Gregorian calendar are as follows:

Month | Number of days |
---|---|

January | 31 |

February | 28/29 |

March | 31 |

April | 30 |

May | 31 |

June | 30 |

July | 31 |

August | 31 |

September | 30 |

October | 31 |

November | 30 |

December | 31 |