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Date & Time Calculators

Date Calculator

Calculate the exact duration between two dates in years, months, weeks, and days, or add and subtract time from any starting date. Includes full business-day counting with automatic US federal and custom holiday skipping.

How the Date Calculator Works

The Date Calculator processes calendar intervals using the standard international Gregorian Calendar. It operates in two primary modes: Days Between Two Dates (calculating exact elapsed time in years, months, weeks, and days) and Add or Subtract Time (adding or subtracting specific time intervals, with optional business-day skipping for weekends and US federal holidays).

The Gregorian Calendar & Leap Year Math

First decreed by Pope Gregory XIII in October 1582 to correct the drift of the Julian calendar relative to solar equinoxes, the Gregorian calendar establishes a mean calendar year of 365.2425 days.

Leap Year Rules

  • Every year that is evenly divisible by 4 is a leap year (adding February 29th)...
  • Except for century years (ending in 00), which are NOT leap years...
  • Unless the century year is also evenly divisible by 400 (for example, 2000 was a leap year, but 1900 was not, and 2100 will not be).

Fixed vs. Floating US Federal Holidays

Business day calculation requires distinguishing between fixed-date holidays and floating-weekday holidays:

Fixed-Date Holidays

Occur on the exact same month and calendar day every year, regardless of weekday.

  • New Year's Day: January 1
  • Juneteenth: June 19
  • Independence Day: July 4
  • Veterans Day: November 11
  • Christmas Day: December 25

Floating-Weekday Holidays

Occur on a specific day of the week relative to the month (e.g. 3rd Monday).

  • MLK Jr. Day: 3rd Monday in January
  • Presidents' Day: 3rd Monday in February
  • Memorial Day: Last Monday in May
  • Labor Day: 1st Monday in September
  • Thanksgiving: 4th Thursday in November

US Federal & Observed Holiday Dates (2026 – 2027)

Reference list of official US federal closures for the current and upcoming calendar years:

Holiday Name2026 Date2027 Date
New Year's DayThu, Jan 1, 2026Fri, Jan 1, 2027
Martin Luther King Jr. DayMon, Jan 19, 2026Mon, Jan 18, 2027
Presidents' DayMon, Feb 16, 2026Mon, Feb 15, 2027
Memorial DayMon, May 25, 2026Mon, May 31, 2027
Juneteenth National Independence DayFri, Jun 19, 2026Sat, Jun 19, 2027 (Observed Jun 18)
Independence DaySat, Jul 4, 2026 (Observed Jul 3)Sun, Jul 4, 2027 (Observed Jul 5)
Labor DayMon, Sep 7, 2026Mon, Sep 6, 2027
Columbus Day / Indigenous Peoples' DayMon, Oct 12, 2026Mon, Oct 11, 2027
Veterans DayWed, Nov 11, 2026Thu, Nov 11, 2027
Thanksgiving DayThu, Nov 26, 2026Thu, Nov 25, 2027
Christmas DayFri, Dec 25, 2026Sat, Dec 25, 2027 (Observed Dec 24)

Frequently Asked Questions

How is the exact duration between two dates calculated?+
The duration between two dates is calculated by comparing calendar years, months, and days using standard calendar borrowing math. For example, if the end day is smaller than the start day, the calculator borrows the exact number of days in the preceding month. The tool also provides a continuous breakdown into total days, total weeks, total hours, total minutes, and total seconds.
How does business-day counting work with holidays?+
Business-day counting calculates elapsed time by skipping Saturdays, Sundays, and any selected official or custom holidays. When adding 10 business days to a Thursday, for instance, the calculator steps forward day-by-day, skipping weekend days and active holidays so that only actual working days are counted toward the total.
What is the difference between fixed and floating US holidays?+
Fixed holidays occur on the exact same month and day every year (e.g. Independence Day is always July 4th, Christmas Day is always December 25th). Floating holidays occur on a specific weekday relative to the month (e.g. Martin Luther King Jr. Day is the 3rd Monday of January; Thanksgiving Day is the 4th Thursday of November). Our calculator automatically computes exact floating holiday dates for any target year.
How are leap years and month-end dates handled when adding months?+
When adding or subtracting months, if the target month has fewer days than the starting day (for example, adding 1 month to January 31st), the calculator automatically rolls back to the last valid day of that target month (February 28th in a standard year, or February 29th in a leap year).
Can I add custom company or regional holidays?+
Yes. In the Holiday Settings drawer, you can add custom recurring holidays by entering a name, month, and day. These custom holidays will be excluded automatically whenever you calculate business-day additions or subtractions.

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