Date Calculator – Calculate Days Between Dates

Gregorian Calendar History

Gregorian is the most widely used calendar system around the world. In Gregorian calendar, an ordinary year comprises of 365 days; however, a leap year will see an additional day added in the month of February. Months of April, June, September, and November contain 30 days each, and all others contain 31 days each; however, the month of February contains 28 days in an ordinary year, and 29 in a leap year.

The Gregorian calendar is a revision of Julian calendar system, which in turn, was a reform of the ancient Roman calendar. Ancient Roman calendar is presumed to have been a lunar calendar as it was based on the moon phase cycle. Later, the Roman people shifted to a 10-month calendar consisting of 304 days, and left the other 50 days unarranged as winter. Due to this reason, it was very hard for them to arrange the winter and summer months correctly, hence the shift to more accurate calendar systems.

The Roman calendar, which was preceded by the Greek calendar, was based on the assumption of 29.5 days for each lunar cycle and 12.5 synodic months in a solar year; however, every four years they coincide, thanks to the introduction of the months of January and February. At this point, there were numerous attempts to bring the Roman calendar into synchronization with the solar year; for example, they would add an additional month in order to balance any year with fewer days. In 46 BC, the Roman calendar underwent another significant reform in terms of the introduction of an algorithm to stop relying on the new moon for determining dates. Caesar managed to bring about synchronization between the two types of timekeeping through the addition of 10 days in the Roman calendar, resulting in a year lasting 365 days, and the introduction of a leap day every four years.

However, even after such reforms, the Julian calendar was still in need of further improvement because of its drift relative to equinoxes and solstices amounting to about 11 minutes each year. By 1582, the calendar had lost 10 days already. Pope Gregory XIII solved the problem of drifting by adding an additional 10 days to the date, with the day following October 4, 1582 becoming October 15. The algorithm of the Julian calendar was also adjusted with regard to century years, which were no longer going to be leap years except those evenly divisible by 400. Thus, the Gregorian calendar brought about correction in the calculation of a year to one day in 128 years, down to 1 day in 3,030 years with reference to the mean solar year.

Adoption of the Gregorian calendar has been going on for several centuries already, and despite many attempts to introduce even more changes into it, today the Gregorian Calendar is still used as the most widespread dating system in the world.

Holidays

A holiday is described as a day that through tradition or statutory means is set aside, and on which the normal routine of attending work or school becomes minimalized. The word "holiday" can be understood to mean something different according to the geographical location being considered. In America, paid vacation leave is often used while national religious or cultural leave days are called "holiday". However, in other geographical locations, especially those that used to be colonized by Britain, "holiday" is often used to describe both paid leaves.

Most holidays commemorate events, personalities or groups of people of particular importance to the culture and religion of the region. While there are a few holidays like Christmas and New Year Day, which are celebrated around the world, each country has its unique set of holidays that are peculiar to the country. Even the celebration of the same holidays in various countries is often different with some giving a total holiday period while others give partial holiday periods. Some countries have holidays that practically put everything to a halt.

The holiday calculator is primarily focused on U.S. holidays but can include other holidays for a certain country. Some holidays may even be selected to be left out of the calculation. For an additional specification, the federal holidays in the U.S. include holidays that have been declared by the United States' government where there are no operations within the non-essential departments in the federal government. Moreover, it includes paid time off for all employees working within the government. However, this is not the case in the private sector where it depends on the preference of the employer whether he or she grants a federal holiday or not. Sometimes, the employee may even be granted holiday pay along with his/her normal salary when working during the holiday period.

Some holidays like New Year’s Day can be considered "fixed holidays" because they always happen on the same day. Other holidays, like Martin Luther King, Jr.'s birthday, are not fixed holidays, as they happen on a "floating Monday," specifically, the third Monday in January. Thanksgiving is another holiday celebrated in the United States, which happens on a "floating Thursday," the fourth Thursday in November, thus making it a non-fixed holiday. Two tables presenting the dates of federal holidays in the United States for 2026 and 2027 are provided below.

2026 U.S. Federal Holidays

2027 U.S. Federal Holidays