How the date calculator works
Each date is turned into a whole day number on the calendar, and the answer is the difference between the two numbers. No clock times are involved, so daylight saving changes and time zones cannot add or lose a day.
Days between two dates
Days = end date − start date (+ 1 if the end date is included)
Weeks = days ÷ 7, with the remainder in days
The years, months and days figure counts whole months forward from the start date, then the days left over.
Worked example: January 15, 2026 to March 20, 2027 is 429 days. That is 61 weeks and 2 days (61 × 7 = 427), or 1 year, 2 months and 5 days: one year takes you to January 15, 2027, two more months to March 15, 2027, and 5 days to March 20.
Business days and federal holidays
Business days are Monday to Friday. With the holiday box ticked, the calculator also takes out the federal holidays set by 5 U.S.C. 6103, on the weekday they are observed. A Saturday holiday is observed the Friday before and a Sunday holiday the Monday after, matching the OPM federal holiday schedule. The 2026 days off are January 1, January 19, February 16, May 25, June 19, July 3, September 7, October 12, November 11, November 26 and December 25.
Worked example: November 1 to November 30, 2026 with the end date included has 21 weekdays. Veterans Day (Wednesday, November 11) and Thanksgiving (Thursday, November 26) fall on weekdays, so there are 19 business days.
The holiday rules used are today’s. Juneteenth is only counted from 2021, when it became a federal holiday; for ranges before 1986, when Martin Luther King, Jr. Day was first observed, the calculator warns that the holiday count may not match that year.
Adding and subtracting
Years and months are added first, then weeks and days. When the new month is too short for the day, the date moves back to the month’s last day: January 31, 2026 plus 1 month is February 28, 2026, and March 31, 2026 minus 1 month is also February 28.
Worked example: October 15, 2026 plus 90 days is Wednesday, January 13, 2027: 16 days to the end of October, 30 in November, 31 in December and 13 in January.
Questions people ask
Does the count include the start and end dates?
By default the result is the number of days from the start date to the end date, the way you would count nights: January 1 to January 31 is 30 days. Tick “Include the end date” to count both days, which gives 31. Weekdays and business days count the start date, and count the end date only when that box is ticked.
Which holidays are left out of business days?
The 11 legal public holidays in 5 U.S.C. 6103: New Year’s Day, Birthday of Martin Luther King, Jr., Washington’s Birthday, Memorial Day, Juneteenth National Independence Day, Independence Day, Labor Day, Columbus Day, Veterans Day, Thanksgiving Day and Christmas Day. Each is taken out on the weekday federal workers get off: a holiday on a Saturday moves to the Friday before (5 U.S.C. 6103(b)) and one on a Sunday to the Monday after (Executive Order 11582), as OPM lists them. State holidays and days such as the Friday after Thanksgiving are not included.
What is January 31 plus one month?
February 28, or February 29 in a leap year. There is no February 31, so when adding months lands on a day the month does not have, the calculator uses the last day of that month and says so. Years and months are added first, then weeks and days, so January 31 plus 1 month and 1 day is March 1, 2026.
Do daylight saving time changes affect the count?
No. The calculator counts calendar dates, not hours, so the night the clocks change still counts as one day. The day count from March 7 to March 9, 2026 is 2 even though clocks went forward on March 8.
How many business days are in 2026?
2026 has 261 weekdays, Monday to Friday. All 11 federal holidays fall on weekdays in 2026 (Independence Day, a Saturday, is observed on Friday, July 3), which leaves 250 business days.
How is the “years, months and days” figure worked out?
It counts whole months from the start date using the same month-end rule as adding months, then the days left over. January 15, 2026 to March 20, 2027 is 1 year, 2 months and 5 days.