Date Calculator

The Gregorian calendar, the calendar system used today throughout most of the world, evolved from the Roman calendar. The Roman calendar, introduced around 750 BCE, had 10 months and 304 days. It was later reformed by Julius Caesar in 46 BCE, creating the Julian calendar with 12 months and 365 days, with a leap day added every four years.

However, the Julian calendar's leap year rule (adding a day every 4 years) was slightly inaccurate, causing the calendar to drift from the solar year. By the 16th century, the calendar was about 10 days out of sync with the seasons.

In 1582, Pope Gregory XIII introduced the Gregorian calendar to correct this drift. The new system:

• Removed 10 days to realign with the solar year
• Modified the leap year rule: years divisible by 100 are not leap years unless also divisible by 400
• This makes the average year 365.2425 days, very close to the actual solar year of 365.2422 days

The Gregorian calendar was gradually adopted by different countries over several centuries. Today, it is the international standard for civil use, though some cultures and religions maintain their own calendar systems for religious or cultural purposes.

Holidays are days designated for celebration, commemoration, or rest. In the United States, federal holidays are established by Congress and apply to federal employees and the District of Columbia. Many states and private employers also observe these holidays.

U.S. federal holidays can be categorized as:

• Fixed holidays: Always occur on the same date each year (e.g., Independence Day on July 4th, Christmas on December 25th)
• Floating holidays: Occur on a specific day of the week in a given month (e.g., Thanksgiving on the fourth Thursday of November, Memorial Day on the last Monday of May)

When calculating business days, holidays are typically excluded along with weekends. This calculator includes U.S. federal holidays in its business day calculations.