History of the Gregorian Calendar

The Gregorian calendar is the most widely used system worldwide today. In this calendar, a typical year has 365 days, with an extra day added to February during a leap year. Specifically, April, June, September, and November have 30 days; the remaining months have 31 days, except for February, which contains 28 days in a common year and 29 days in a leap year.

This calendar evolved from the Julian calendar—a reform of the ancient Roman calendar. Originally, the Roman calendar was based on lunar observations, tracking the phases of the moon. Later, the Romans adopted a 10-month calendar totaling about 304 days, leaving roughly 50 unorganized days during winter. This misalignment of seasons eventually spurred the development of more accurate systems.

The subsequent Republican calendar, influenced by Greek methods, assumed a lunar cycle of roughly 29.5 days and around 12.5 synodic months per solar year. To synchronize the lunar and solar cycles, intercalary months (January and February) were periodically added. Despite various adjustments, the system needed refinement until Julius Caesar reformed it in 46 BC. By inserting 10 extra days into the calendar, he established a 365-day year with a leap day every fourth year, eliminating the reliance on lunar observations.

However, the Julian calendar still drifted approximately 11 minutes per year relative to the solar cycle. By 1582, this discrepancy amounted to a 10-day error. Pope Gregory XIII resolved the issue by skipping 10 days—making October 15, 1582, follow immediately after October 4—and adjusting the leap year rule. Under the Gregorian system, century years not divisible by 400 are not leap years, reducing the error to about one day every 3,030 years. Although its adoption was gradual, the Gregorian calendar remains the global standard today.

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Holidays

A holiday is a designated day set aside by custom or law during which regular activities like work or school are reduced or suspended. The definition of a holiday can vary by region. In the United States, the term “holiday” typically refers to national, religious, or cultural observances, while paid leave is often called “vacation.” In other regions, such as the United Kingdom, “holiday” may refer to both types of days off.

Holidays are usually established to commemorate significant events, individuals, or cultural and religious traditions. While globally celebrated holidays like Christmas and New Year’s Day are observed in many countries, each nation typically has its own unique set of holidays. Observance can vary widely—even for the same holiday—with some regions fully suspending work and others only offering partial days off. In certain countries, like Brazil during Carnaval, holidays can lead to nearly a complete shutdown of non-essential activities.

This date calculator primarily focuses on U.S. holidays, although users can manually input holidays specific to other regions or choose to exclude certain days. In the United States, federal holidays are officially recognized by the government, leading to the closure of non-essential federal offices and paid leave for federal employees. However, private-sector observance is determined by individual employers.

Some holidays, such as New Year’s Day, are fixed and occur on the same date every year. Others, like Martin Luther King Jr. Day (observed on the third Monday in January) or Thanksgiving (observed on the fourth Thursday in November), have floating dates that vary each year. Below are the U.S. federal holidays for 2025 and 2026:

2025 U.S. Federal Holidays

• New Year’s Day: Jan. 1, 2025
• Martin Luther King Jr. Day: Jan. 20, 2025
• President’s Day: Feb. 17, 2025
• Memorial Day: May 26, 2025
• Juneteenth Day: Jun. 19, 2025
• Independence Day: Jul. 4, 2025
• Labor Day: Sep. 1, 2025
• Columbus Day: Oct. 13, 2025
• Veteran’s Day: Nov. 11, 2025
• Thanksgiving: Nov. 27, 2025
• Christmas: Dec. 25, 2025

2026 U.S. Federal Holidays

• New Year’s Day: Jan. 1, 2026
• Martin Luther King Jr. Day: Jan. 19, 2026
• President’s Day: Feb. 16, 2026
• Memorial Day: May 25, 2026
• Juneteenth Day: Jun. 19, 2026
• Independence Day: Jul. 4, 2026
• Labor Day: Sep. 7, 2026
• Columbus Day: Oct. 12, 2026
• Veteran’s Day: Nov. 11, 2026
• Thanksgiving: Nov. 26, 2026
• Christmas: Dec. 25, 2026

This comprehensive overview provides insight into the evolution of our modern calendar and the significance of holidays, helping you better understand how these systems shape our everyday lives.