Date Calculator

History of the Gregorian Calendar

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

The Gregorian calendar was introduced as a reform of the Julian calendar, which itself was based on the ancient Roman calendar. The Roman calendar was believed to be a lunar calendar, based on the phases of the moon. Early Romans used a 10-month calendar with 304 days, leaving about 50 days of unaccounted winter. This system led to the misalignment of the seasons, prompting the need for a more accurate calendar.

The Roman Republican calendar later followed Greek models, assuming that the lunar cycle was 29.5 days and that 12.5 lunar months made up a solar year. The addition of intercalary months, like January and February, helped align the calendar with the solar year. Over time, various modifications were made, including adding extra months in some years to account for discrepancies. In 46 BC, Julius Caesar reformed the calendar by eliminating the reliance on moon sightings. He added 10 days to the calendar, making the total number of days in a year 365. He also introduced a leap year every four years, further aligning the calendar with the solar year.

Despite these reforms, the Julian calendar still had issues. The calendar drifted by approximately 11 minutes each year, leading to a 10-day discrepancy by 1582. Pope Gregory XIII addressed this by skipping 10 days in the calendar—October 4, 1582, was followed by October 15, 1582. He also changed the leap year rule, stating that century years not divisible by 400 would not be leap years. This adjustment reduced the error from 1 day in 128 years to 1 day in 3,030 years.

The Gregorian calendar was gradually adopted over several centuries and, despite various proposals for further reforms, remains the most commonly used calendar system worldwide.

Holidays

A holiday is a day set aside for rest or celebration, during which regular activities like work or school are typically paused or reduced. The term "holiday" can mean different things depending on the region. In the U.S., paid time off for vacation is usually called "vacation," while national, religious, or cultural observances are referred to as "holidays." However, in some regions, like the United Kingdom or former British colonies, "holiday" can also mean paid leave.

Holidays are often tied to significant events, people, or cultural or religious traditions. While some holidays, such as Christmas and New Year's Day, are celebrated globally, each country often has its own unique holidays. Even within a country, holidays may be observed differently: some may involve a full suspension of work and school, while others might result in only partial time off. For example, in Brazil, Carnaval lasts almost a week, during which only certain businesses like industrial and carnival-related ones operate.

This calculator primarily focuses on U.S. holidays, though you can manually input holidays from other countries. Certain holidays can also be excluded if needed. Federal holidays in the U.S. are recognized by the government, meaning non-essential federal government offices are closed, and federal employees typically receive paid leave. However, this doesn't always apply in the private sector, where companies have discretion over which holidays to observe, and employees may receive additional holiday pay if they work on these days.

Some holidays, like New Year's Day, are "fixed holidays" because they occur on the same date each year. Others, such as Martin Luther King Jr.'s birthday, are "floating holidays," meaning they occur on a specific weekday in a given month (e.g., the third Monday in January). Thanksgiving is another example of a floating holiday in the U.S., observed on the fourth Thursday in November, which means its date changes each year.

Below are the dates for U.S. federal holidays in 2025 and 2026: