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History of the Gregorian Calendar

The Gregorian calendar is the most widely used calendar today. A standard year in this calendar has 365 days, with an extra day added to February during leap years. April, June, September, and November have 30 days each, while the other months have 31 days, except for February, which has 28 days in a standard year and 29 in a leap year.

The Gregorian calendar is a reformed version of the Julian calendar, which was itself a modification of the ancient Roman calendar. The ancient Roman calendar was believed to be a lunar calendar based on the moon’s phases. Initially, the Romans used a 10-month calendar with 304 days, leaving the remaining days of winter unorganized. This misalignment led to the adoption of more accurate calendars.

The Republican calendar, later used by Rome, assumed 29.5 days in a lunar cycle and 12.5 synodic months in a solar year, aligning every fourth year with the addition of intercalary months of January and February. Over time, attempts were made to synchronize the Republican calendar with the solar year, including adding an extra month to certain years. In 46 BC, Julius Caesar reformed the calendar, making it independent of lunar observations by adding 10 days, making a total of 365 days in a year, and introducing a leap day every four years to better align with the solar year.

Despite these efforts, the Julian calendar still drifted by approximately 11 minutes per year. By 1582, this discrepancy resulted in a 10-day difference. Pope Gregory XIII addressed this by skipping 10 days, making October 4, 1582, followed by October 15. He also revised the leap year rule, making century years not divisible by 400 non-leap years. This adjustment reduced the error to 1 day in 3,030 years relative to the mean solar year.

The Gregorian calendar’s adoption was gradual over centuries, and despite many proposals for further reform, it remains the most widely used dating system worldwide.

Holidays

A holiday is a day set aside by custom or law for suspension or reduction of regular activities like work or school. The term “holiday” varies by region. In the U.S., paid leave is called “vacation,” while national, religious, or cultural days off are termed “holidays.” In the UK and former British colonies, “holiday” can also mean paid leave.

Holidays often commemorate significant events, people, or cultural and religious practices. While some holidays like Christmas and New Year’s Day are celebrated globally, most countries have unique holidays, and even the same holidays can be observed differently within countries. For example, Brazil’s Carnaval do Brasil nearly shuts down the country for a week, with only essential businesses operating.

This calculator focuses on U.S. holidays, but holidays specific to any country can be added manually, and certain holidays can be excluded. In the U.S., federal holidays are recognized by the government, closing non-essential federal offices and granting paid leave to federal employees. Private sector observance of federal holidays varies by company, and employees working on a federal holiday may receive additional holiday pay.

Some holidays, like New Year’s Day, are “fixed holidays” occurring on the same date each year. Others, like Martin Luther King Jr. Day, are “floating” holidays that fall on specific days of the week, such as the third Monday in January. Thanksgiving, another widely observed U.S. holiday, is a “floating Thursday,” celebrated on the fourth Thursday in November. Below are tables showing the dates of U.S. federal holidays for 2024 and 2025. check the tool date to date calculate