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History of the Gregorian Calendar

The Gregorian calendar is the most prevalently used calendar today. Within this calendara standard year consists of 365 days with a leap day being introduced to the month of February during a leap year. The months of AprilJuneSeptemberand November have 30 dayswhile the rest have 31 days except for Februarywhich has 28 days in a standard yearand 29 in a leap year.

The Gregorian calendar is a reformed version of the Julian calendarwhich was itself a modification of the ancient Roman calendar. The ancient Roman calendar was believed to be an observational lunar calendarbased on the cycles of the moon's phases. The Romans were then believed to have adopted a 10-month calendar with 304 daysleaving the remaining 50 or so days as an unorganized winter. This calendar allowed the summer and winter months to become completely misplacedleading to the adoption of more accurate calendars.

The Republican calendar later used by Rome followed Greek calendars in its assumptions of 29.5 days in a lunar cycle and 12.5 synodic months in a solar yearwhich align every fourth year upon the addition of the intercalary months of January and February. From this pointmany attempts were made to align the Republican calendar with the solar year including the addition of an extra month to certain years to supplant the lack of days in a particular year. In 46 BCthe calendar was further reformed by Julius Caesarintroducing an algorithm that removed the dependence of calendars from the observation of the new moon. In order to accomplish thisCaesar inserted an additional 10 days into the Republican calendarmaking the total number of days in a year 365. He also added the intercalation of a leap day every fourth yearall in an attempt to further synchronize the Roman calendar with the solar year.

Despite all effortsthe Julian calendar still required further reformsince the calendar drifted with respect to the equinoxes and solstices by approximately 11 minutes per year. By 1582this resulted in a difference of 10 days from what was expected. Pope Gregory XIII addressed this by essentially skipping 10 days in the datemaking the day after October 41582October 15. An adjustment was also made to the algorithm of the Julian calendar that changed which century years would be considered leap years. Under the Gregorian calendarcentury years not divisible by 400 would not be leap years. These changes reduced the error from 1 day in 128 yearsto 1 day in 3,030 years with respect to the current value of the mean solar year.

The adoption of the Gregorian calendar occurred slowly over a period of centuriesand despite many proposals to further reform the calendarthe Gregorian Calendar still prevails as the most commonly used dating system worldwide.

Holidays

A holiday is a day thateither by custom or by lawis set aside such that regular activities like going to work or school are suspendedor at least reduced. The term "holiday" can be interpreted differentlydepending on the region. In the U.S.paid leave is typically referred to as "vacation," while nationalreligiousor cultural days off are referred to exclusively as "holiday." In some regionshoweversuch as the United Kingdom or former British coloniesthe term holiday can also refer to paid leave.

Generallyholidays are meant to commemorate some eventpersonor group of cultural or religious significance. Although certain holidayssuch as Christmas and New Year's Dayare widely celebrated worldwidemost countries have their own set of holidays that are specific to the countryand even the same holidays may be observed differently within countries: some may receive a full suspension of typical daily activitieswhile others may only get partial days off. Certain countries have holidays that essentially shut down almost all businesses. As an examplein BrazilCarnaval do Brasil results in almost a full week in which only industrial productionretail establishmentsor carnival-related businessesfunction.

This calculator is mainly geared towards U.S. holidaysbut holidays specific to a given country can be entered manually. Certain holidays can also be excluded. For a further level of specificityfederal holidays in the U.S. refer to holidays that have been recognized by the U.S. government; on these daysnon-essential federal government offices are closedand all federal employees receive paid leave. This is not necessarily true in the private sectorhoweverand which federal holidays a private sector employee receives is largely dependent on the discretion of the company. In some casesan employee who is required to work on a federal holiday may receive compensation in the form of holiday pay in addition to their regular wages.

Certain holidays such as New Year's Day are referred to as "fixed holidays," since they fall on the same date every year. Otherssuch as the birthday of Martin Luther KingJr.don't have a fixed datebecause they occur on a "floating Monday"; in this particular casethe holiday occurs on the third Monday of January. Another widely observed holiday in the U.S.Thanksgivingoccurs on a "floating Thursday," the fourth Thursday In Novemberhence the dates of these holidays vary by year. Below are two tables showing the dates of federal holidays in the U.S. for 2026 and 2027.

2026 U.S. Federal Holidays

2027 U.S. Federal Holidays