What day of the week was 9/11/01?

September 11, 2001 was a Tuesday. It was the 254th day of 2001, with 111 days left in the year. Click the 9/11 button under Famous Dates to see the full result.

What day of the week was December 5, 1987?

December 5, 1987 was a Saturday, the 339th day of 1987.

What day of the week was September 5, 1776?

September 5, 1776 was a Thursday under Gregorian rules, which Britain and its American colonies had used since 1752. For older dates recorded in the Julian calendar, switch the calendar rules to Julian.

How far back does this calculator work?

It uses integer calendar arithmetic rather than the JavaScript Date parser and accepts years 1 through 9999. The result depends on whether Gregorian or Julian rules are selected.

Does it account for the Gregorian calendar reform?

Yes. Choose "Julian until 1582" for Spain, Portugal, Italy, Poland and most Catholic countries (Thursday, October 4, 1582 was followed by Friday, October 15), or "Julian until 1752" for Britain and its American colonies (Wednesday, September 2, 1752 was followed by Thursday, September 14). Dates in the skipped gap are rejected, and the result shows the same day in the other calendar. Other countries switched on other dates, so for them pick Julian or Gregorian to match your source.

What day of the week was October 12, 1492?

Columbus's landfall on October 12, 1492 was recorded in the Julian calendar, where it was a Friday. The same day in the proleptic Gregorian calendar is October 21, 1492. Select "Julian until 1582" and enter the date to see both.

Why did Shakespeare and Cervantes die on the same date but not the same day?

Both are recorded as dying on April 23, 1616, but England still used the Julian calendar while Spain had switched to the Gregorian. Shakespeare's April 23 (Julian) was a Tuesday, May 3 in Gregorian terms, ten days after Cervantes's Saturday, April 23 (Gregorian).

What is Zeller's congruence?

Zeller's congruence is a mathematical algorithm devised by Christian Zeller in 1882 to calculate the day of the week for any date in the Gregorian or Julian calendar using only integer arithmetic.

Why does entering month 1 or 2 shift the year?

In Zeller's algorithm, January and February are treated as months 13 and 14 of the previous year. The tool handles this internally — just enter the real month number.

Can I look up future dates?

Yes. The algorithm works for any valid date, past or future, as long as the year is between 1 and 9999.

Day of Week in History

Enter a date to find its weekday. For history, pick the 1582 (Catholic Europe) or 1752 (Britain and its colonies) switch so older dates use the Julian calendar; the result shows the same day in the other calendar, a month calendar and years with the same weekday.

September 11, 2001 (9/11/01) was a Tuesday.

Enter a Date

Month

Day

Year

Calendar rules

For old documents, pick the switch used where the date was recorded. Dates skipped by the reform are rejected.

Famous Dates

Enter a date and click Find Day of Week

Calendar scope, method, and privacy

Proleptic Gregorian mode extends current Gregorian rules to every supported year. Julian mode applies Julian leap-year and weekday rules. This tool does not automatically model country-specific calendar adoption or omitted reform dates.

Calculations use integer calendar arithmetic in your browser. Dates are not sent to an external calculation service or stored by this tool.

References: U.S. Naval Observatory Julian dates and NIST calendar resources.

Copied!

Quick answer

September 11, 2001 (9/11/01) was a Tuesday. It was day 254 of 2001, a common year of 365 days; September 11 fell on a Tuesday again in 2007, 2012 and 2018.

Examples

Date	Day of the week
September 11, 2001	Tuesday
December 5, 1987	Saturday
November 9, 1989	Thursday
July 20, 1969	Sunday
June 6, 1944	Tuesday

Enter any date, years 1–9999, and copy the weekday with one click.

Summary

This tool calculates the weekday for a date from year 1 to 9999 with integer calendar arithmetic. Proleptic Gregorian mode applies today's Gregorian leap-year rules to all years. Julian mode applies the older calendar. Two historical modes switch automatically: Julian until October 4, 1582 then Gregorian from October 15, 1582 (the papal reform), or Julian until September 2, 1752 then Gregorian from September 14, 1752 (Britain and its colonies). Each result adds the same day in the other calendar, the Julian Day Number, the ISO week, the day count from today and a calendar of the month.

How it works

Enter a year, month, and day in the input fields.
Choose proleptic Gregorian or Julian calendar rules.
The tool applies the corresponding Zeller congruence using integer arithmetic.
January and February are internally shifted to months 13–14 of the prior year.
The result is mapped to a weekday name (Sunday through Saturday).
The date is also converted to a Julian Day Number, which gives the equivalent date in the other calendar, the ISO week and the exact number of days from today.
The formatted date, day name, month calendar and nearby matching years are displayed instantly.

Use cases

Verify what day of the week a historical event occurred on.
Check the weekday of a birthday or anniversary in any past year.
Confirm the day of a contract, document, or legal date.
Satisfy curiosity about famous dates like the moon landing or D-Day.
Plan future dates by confirming which day a year-out date will be.
Research genealogy dates to understand weekly schedules of the era.

Frequently Asked Questions

Last updated: 2026-10-09 · Reviewed by Nham Vu