How we count

This page describes every rule behind the numbers on DayReckon. If a result looks wrong, this is where to check our method before you check our arithmetic.

What does "today" mean?

There are two clocks on each page.

• The page text (title, answer box, tables) is rebuilt once a day, shortly after midnight in New York (America/New_York). Those numbers use Eastern time.
• The live counter recalculates in your browser with your device's clock and time zone. Late in the evening in the Pacific or Hawaii zones, the two can differ by one day. The live counter is right for where you are.

How do we count days between two dates?

The start date is day zero and is not counted. Monday to Tuesday is 1 day. This is the countdown convention: the count reaches zero on the target date. When a rule counts both ends (inclusive), the days-between calculator can add the last day.

Days are counted on the calendar in whole dates, so daylight saving time does not change a day count. Live counters that show hours and minutes use real elapsed time to the target instant, so they stay right across the 23-hour and 25-hour days in March and November.

How do we count weeks, weekends and months?

• Weeks are days divided by 7, with the remainder shown as extra days.
• Weekends are the Saturdays strictly between today and the target date.
• Months step forward one calendar month at a time with the same day number. If that day does not exist, the step stops at the month's last day, so one month after January 31 is February 28 (or 29). Leftover days are counted after the last whole month.
• Leap years follow the Gregorian rule: divisible by 4, except century years not divisible by 400.

How do we count business days?

A business day is Monday to Friday, minus the federal holidays named in 5 U.S.C. 6103, on the observed dates published by the Office of Personnel Management. A Saturday holiday is observed on the Friday before and a Sunday holiday on the Monday after. When counting business days from a date, the start date is not counted and the end date is. State holidays, company closures and the Federal Reserve's different Saturday rule are not included; pages that discuss them say so.

Where do the dates come from?

• Federal holidays: OPM, checked against a second published calendar.
• Seasons (equinoxes and solstices): the US Naval Observatory, in UTC, checked against an independent ephemeris and converted to each US time zone.
• Meteorological seasons: the whole-month definition described by NOAA.
• Easter: the US Census Bureau Easter table, checked against our own calculation with the Anonymous Gregorian algorithm.
• Daylight saving time: the rule described by NIST: second Sunday in March to first Sunday in November, at 2:00 a.m. local time.
• Ramadan and Eid al-Fitr: the Fiqh Council of North America calendar, checked against a second published table. These are always labeled expected, because the actual start depends on the moon.
• School calendars: each district's own published calendar, one row per district. A district we cannot read at the source is left out, not filled from another website.
• Events: the organizer's own announcement, plus a second report. Times that have not been announced are shown as not announced.
• Sunrise and sunset: calculated by us with the NOAA solar position equations for each city's coordinates. Expect a minute or two of difference from an observatory table.

Every date is opened at its source, and the source is logged before the date is published. If we can confirm a date in only one place, it does not appear on a page; the page says what is missing instead.

How often is it updated?

• Day counts: every day, automatically.
• Holiday dates: each year after OPM publishes, and whenever a source changes.
• Seasons and Easter: fixed years ahead, rechecked once a year.
• Shipping deadlines, event times and school calendars: when the carrier, organizer or district publishes.

The "Checked" line under each page title shows the date of the last review and what changed.