Date Calculator

Date Calculator – Calculate Date Difference & Add or Subtract Days

This Date Calculator helps you calculate the difference between two dates or add and subtract days from a specific date. It is useful for planning events, calculating deadlines, tracking durations, and understanding calendar-based time gaps accurately.

History of the Gregorian Calendar

The Gregorian calendar is the most widely used calendar system today. A standard year consists of 365 days, with an extra leap day added to February during leap years. April, June, September, and November have 30 days, while the remaining months have 31 days, except February.

The Gregorian calendar was introduced in 1582 as a reform of the Julian calendar. It corrected long-term drift caused by inaccuracies in the older system and improved alignment with the solar year.

From Roman Calendar to Modern Dating System

Early Roman calendars were lunar-based and highly inaccurate. Over time, reforms introduced by Julius Caesar created the Julian calendar with 365 days and leap years.

However, the Julian calendar drifted by about 11 minutes per year. This led Pope Gregory XIII to introduce the Gregorian calendar by skipping 10 days in October 1582 and modifying leap-year rules for century years.

Holidays and Date Calculations

Holidays can significantly affect date calculations, especially when calculating working days or deadlines. A holiday is a day officially recognized by law or tradition when normal activities are reduced or suspended.

In the United States, federal holidays apply to government employees, while private-sector holiday policies vary. This calculator allows holidays to be included or excluded for more accurate results.

Fixed and Floating Holidays

• Fixed holidays occur on the same date every year (e.g., New Year’s Day)
• Floating holidays occur on specific weekdays (e.g., Thanksgiving)

Floating holidays change dates each year, making date calculators especially useful for planning.

U.S. Federal Holidays (2026 & 2027)