Date & Day Calculator

Enter a date and see which day of the week it is

February 29, 2024 was a Thursday, January 1, 2000 was a Saturday, and December 25, 2026 falls on a Friday. Type a year, month and day into the calculator above and it shows the weekday along with whether the date is a weekday, a weekend day or a federal holiday, which weekday of the month it is (such as the 4th Thursday), where it sits in the year, the ISO week number and whether the year is a leap year.

Below the result you will find a strip showing the same date across the 10 years before and after, and a step-by-step Zeller's congruence solution for working out a weekday by hand. Enter a birthday to see the weekday you were born on and the weekday of this year's and next year's birthday.

When you need to check the weekday

Flipping through a calendar works for next month, but not for a date 30 years back or 5 years ahead. A weekday can also change a real schedule or deadline.

• What day of the week was I born? Someone born on May 15, 1990 was born on a Tuesday. The strip shows that the birthday falls on a Friday in 2026 and a Saturday in 2027.
• Thanksgiving and other "nth weekday" dates: Thanksgiving is the fourth Thursday in November (5 U.S.C. 6103(a)), which is November 26 in 2026 and November 25 in 2027. Enter either date and the calculator reports "4th Thursday of November." Washington's Birthday (third Monday in February) and Columbus Day (second Monday in October) work the same way.
• A deadline that lands on a weekend: in federal civil cases, Rule 6(a)(1) of the Federal Rules of Civil Procedure has you exclude the day of the triggering event, count every day including weekends and legal holidays, and include the last day. If the last day is a Saturday, Sunday or legal holiday, the period continues to run until the end of the next day that is not one of those. For example, 30 days after Thursday, October 29, 2026 is Saturday, November 28, so the deadline moves to Monday, November 30.
• Holidays that move to a weekday: Independence Day 2026 is a Saturday, and OPM lists Friday, July 3 as the observed federal holiday. Checking the weekday first tells you whether a holiday will shift.
• Writing the date on a form or in a file name: copy the ISO format (2024-02-29) or the ISO week (2024-W09-4) as is.

How the calculation works

1. Weekday: the date is converted to a count of days from a fixed reference day, and the remainder after dividing by 7 gives the weekday. Everything is computed at 00:00 UTC, so your device's time zone never changes the result.
2. Leap year: a year divisible by 4 is a leap year, except that years divisible by 100 are common years unless they are also divisible by 400. So 1900 and 2100 are common years and 2000 is a leap year.
3. Day of the year and days left: January 1 is day 1. Days left counts from the day after the date through December 31.
4. Which weekday of the month: days 1-7 are the 1st, 8-14 the 2nd, 15-21 the 3rd, 22-28 the 4th and 29-31 the 5th. If adding 7 days would move into the next month, it is the last of that weekday in the month.
5. ISO week: under ISO 8601, weeks start on Monday and week 1 is the week containing the year's first Thursday. January 4 is therefore always in week 1. This is different from the U.S. habit of starting weeks on Sunday.
6. Federal holidays: for 2026 and 2027 the calculator marks the federal holidays with the observed dates published by the U.S. Office of Personnel Management. Other years separate only Saturdays and Sundays.
7. Unix time: the seconds from 00:00 UTC on January 1, 1970 to 00:00 UTC on that date. February 29, 2024 is 1,709,164,800. Midnight in New York (Eastern Standard Time, UTC−5) that day is 5 hours (18,000 seconds) later: 1,709,182,800.

Finding the weekday by hand: Zeller's congruence

In 1887 the German mathematician Christian Zeller published formulas for finding the weekday from a date alone (Kalender-Formeln, Acta Mathematica). For the Gregorian calendar the formula is:

h = (q + ⌊13(m+1)/5⌋ + K + ⌊K/4⌋ + ⌊J/4⌋ + 5J) mod 7

Here q is the day of the month, m is the month, K is the last two digits of the year and J is the first two. January and February count as months 13 and 14 of the previous year. The brackets ⌊ ⌋ mean rounding down. A remainder h of 0 means Saturday, 1 Sunday, and 6 Friday.

If the formula feels heavy, count the shift instead. A common year has 365 days, which is 52 weeks and 1 day, so a date falls one weekday later the next year. If a February 29 falls in between, it moves two weekdays. For example, October 17, 2026 is a Saturday, October 17, 2027 is a Sunday, and October 17, 2028 is a Tuesday because February 29, 2028 comes in between. The year strip in the calculator marks those two-day jumps with "+2."

Weekdays of key U.S. dates, 2026-2035

New Year's Day, Independence Day, Halloween, Thanksgiving and Christmas Day. Thanksgiving is always a Thursday, so the table gives its date. Holidays defined as a Monday, such as Memorial Day and Labor Day, are left out.

Years that reuse the same calendar

When two years begin on the same weekday and are both leap years or both common years, every date falls on the same weekday in both. A common year usually repeats after 6 or 11 years, a leap year after 28 years (passing a century year such as 2100, which is not a leap year, breaks the pattern).

The Gregorian calendar repeats exactly every 400 years, which is 146,097 days or 20,871 whole weeks. Over those 400 years the 13th of the month falls 4,800 times: on a Friday 688 times, the most often, and on a Thursday or Saturday 684 times each, the least often.

When the ISO week year differs from the calendar year

ISO assigns each week to the year that contains its Thursday, so a few days at the turn of the year can belong to the neighboring year's week numbering. 2026 begins on a Thursday, so it has 53 weeks.

Common mistakes

• Reading 03/04/2026 the wrong way: in the United States it means March 4, but in much of the world it means April 3. This calculator takes the year, month and day in separate fields, so nothing is ambiguous. Write 2026-03-04 when you share a date with someone abroad.
• Treating 1900 as a leap year: Microsoft Excel treats 1900 as a leap year to stay compatible with Lotus 1-2-3 serial dates, and Microsoft notes that the WEEKDAY function returns incorrect results for dates before March 1, 1900. In reality 1900 was a common year, there was no February 29, 1900, and March 1, 1900 was a Thursday.
• Mixing up "week of the month" and the ISO week: the week of the month depends on whether weeks start on Sunday or Monday. The "nth weekday" in this calculator depends only on the date. The ISO week always starts on Monday.
• Ignoring time zones: the weekday depends on the local time. When it is Monday 8:00 a.m. in Tokyo, it is still Sunday 7:00 p.m. in New York while daylight saving time is in effect. For a deadline abroad, enter the date as it is in that place.
• Assuming an observed holiday is the holiday itself: when a federal holiday falls on a Saturday, the Friday before is generally the observed holiday for employees on a Monday-Friday schedule, and OPM's list shows these observed dates. The calculator marks the observed date for 2026 and 2027.

What this calculator does not cover

• The Gregorian calendar was first introduced in 1582, so the calculator accepts Gregorian dates from 1583 to 9999 only. Countries adopted it at different times. Great Britain did so by act of Parliament in 1752: the day after September 2, 1752 was counted as September 14, omitting 11 days. Dates from before a country's changeover are recorded in the older Julian calendar and will not match the weekday shown here.
• Holidays are the 11 federal holidays for 2026 and 2027. State holidays, employer-specific days off, market closures and holidays that may be declared later are not included.
• Rule 6(a) is a federal civil procedure rule. State courts, administrative agencies, contracts and other statutes may count time differently, and state holidays can matter for some periods. Confirm the actual deadline with the court, agency or counsel handling it. This page is not legal advice.
• "Today" and "days from today" use the date on your device.

Basis Dates use the Gregorian calendar. The examples and tables on this page were calculated on October 17, 2026.

Sources

• 01Cornell Legal Information Institute: Federal Rules of Civil Procedure, Rule 6, Computing and Extending TimeRule 6(a)(1) and 6(a)(6), opened October 17, 2026
• 02U.S. Government Publishing Office: 5 U.S.C. 6103, HolidaysHoliday dates in subsection (a), opened October 17, 2026
• 03U.S. Office of Personnel Management: Federal Holidays2026 and 2027 observed dates
• 04legislation.gov.uk: Calendar (New Style) Act 1750Section 1 heading: 2 September 1752 followed by 14 September, omitting 11 days
• 05ISO: ISO 8601 Date and time format
• 06U.S. Naval Observatory (USNO): Introduction to CalendarsGregorian calendar introduced in 1582 and its leap year rule
• 07Chr. Zeller, Kalender-Formeln, Acta Mathematica 9 (1887), 131–136
• 08Microsoft Learn: Excel incorrectly assumes that the year 1900 is a leap year

Frequently asked questions

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