Calendar sources
Holiday dates come from official rules. Counts and breakdowns are calculated from the dates you choose.
Updated
Dates and rules
The holiday list below links each rule to its official reference. The downloadable calendar rules contain the same references and read dates, so the rule stays with the date.
Use of official calendar facts
The published US holiday rules are calendar facts drawn from United States Government sources. The original government material is public domain where applicable. Our numbers are calculated from the official rules below. We do not copy results from other sites.
Calendar arithmetic
Gregorian leap-year rules and Easter calculations follow the US Naval Observatory references below. Date-to-day conversion uses Howard Hinnant’s public-domain civil-date algorithms. All examples and derived totals are our own arithmetic.
What this holiday list covers
This list describes recurring dates. It does not promise every closure in every workplace. Keep actual and observed dates distinct. Astronomical times are stored separately at the precision published by the Observatory.
A missing or changed rule
The US federal calendar excludes state holidays and one-off closures. Check the original authority for a consequential deadline. We cannot take corrections yet. When that opens, the contact page will say so.
Holiday rules and references
Birthday of Martin Luther King, Jr.
Third Monday in January. Used by the recurring federal working-day calendar.
Washington's Birthday
Third Monday in February. Used by the recurring federal working-day calendar.
Memorial Day
Last Monday in May. Used by the recurring federal working-day calendar.
Juneteenth National Independence Day
June 19. Used by the recurring federal working-day calendar.
Labor Day
First Monday in September. Used by the recurring federal working-day calendar.
Columbus Day
Second Monday in October. Used by the recurring federal working-day calendar.
Thanksgiving Day
Fourth Thursday in November. Used by the recurring federal working-day calendar.
Easter Sunday
Gregorian Easter Sunday, calculated separately for each year. Not removed as a federal working day.
Christmas Eve
December 24. Not removed as a federal working day.
Original holiday references
- US federal holiday law · Read 2026-09-19. Public domain as a work of the United States Government (17 U.S.C. 105).
- USNO Gregorian Easter rules · Read 2026-09-19. Public domain as a work of the United States Government (17 U.S.C. 105).
- Census Halloween date · Read 2026-09-19. Public domain as a work of the United States Government (17 U.S.C. 105).
- Census Valentine's Day date · Read 2026-09-19. Public domain calendar fact from a United States Government source.
- National Park Service Christmas Eve date · Read 2026-09-19. Public domain calendar fact from a United States Government source.
Counting conventions
Leap years and month lengths
Gregorian leap years and month lengths
USNO Gregorian calendar rules · Read 2026-09-19. Government calendar facts.
Days between calendar dates
Counting days between two calendar dates
Civil-date arithmetic by Howard Hinnant · Read 2026-09-19. Public-domain algorithm.
Adding months and counting age
Adding months and years, including month ends, and counting age in years, months and days
Month and year counting conventions · Read 2026-09-19. Our own arithmetic, following these counting conventions.
Timezones and clock changes
Named timezones, nonexistent and repeated local times
Timezone and repeated-time conventions · Read 2026-09-19. The date library uses the ISC licence.
Week numbers
ISO weekday and week-year definitions; Sunday-start alternative is explicitly defined by this site
ISO weekday and week-year definitions · Read 2026-09-19. Publicly available definition; no document reproduced.
Converting time units
Minutes, hours and nominal days; our arithmetic: week = 7 days, mean Gregorian year = 146097 / 400 days, mean month = mean year / 12. The largest conversion is limited to 9,007,199,254,740,991 seconds so whole seconds can still be represented exactly.
BIPM definitions of minutes, hours and days · Read 2026-09-19. Published unit definitions; derived figures are our arithmetic.
Worked examples
Worked examples use the dates and choices shown on each page; the totals are our own arithmetic.
How we count days · Read 2026-09-19. Original arithmetic.
Astronomical seasons
Northern Hemisphere equinoxes and solstices are stored for 2026 through 2031. Each time is published to the minute in Universal Time and converted to the timezone you choose. At this precision the site treats Universal Time as UTC.
US Naval Observatory season times for 2026 · Read 2026-09-19.
US Naval Observatory season times for 2027 · Read 2026-09-19.
US Naval Observatory season times for 2028 · Read 2026-09-19.
US Naval Observatory season times for 2029 · Read 2026-09-19.
US Naval Observatory season times for 2030 · Read 2026-09-19.
US Naval Observatory season times for 2031 · Read 2026-09-19.
Download the recurring US holiday rules as JSON. For the meaning of each count, see how we count days.