What Day of the Week Was September 11, 2001?
September 11, 2001 (9/11) was a Tuesday. On the morning of September 11, 2001, hijacked airliners struck the World Trade Center in New York and the Pentagon near Washington, and a fourth plane crashed near Shanksville, Pennsylvania.
September 11, 2001 is a Tuesday
- Day of the year:
- day 254 of 365, 111 days left in the year
- Week number:
- ISO week 37 of 2001 · US week 37
- Weekday number:
- 3 in the US (Sunday = 1) · 2 in ISO 8601 (Monday = 1)
Another date? Change the date above, or open the day of the week calculator for today's weekday and any other date.
September 11, 2001 in numbers
| September 11, 2001 | |
|---|---|
| Day of the week | Tuesday |
| Weekday number | 3 in the US (Sunday = 1), 2 in ISO 8601 (Monday = 1) |
| Day of the year | 254 of 365, 111 days left |
| ISO week | Week 37 of 2001 |
| US week | Week 37 |
| Leap year | No, 2001 had 365 days |
| Julian Day Number | 2452164 |
September 2001 calendar
The whole month, with September 11, 2001 highlighted and the US federal holidays marked. The column on the left is the US week number.
| Wk | Su | Mo | Tu | We | Th | Fr | Sa |
|---|---|---|---|---|---|---|---|
| 35 | 1 | ||||||
| 36 | 2 | 3 (Labor Day) | 4 | 5 | 6 | 7 | 8 |
| 37 | 9 | 10 | 11 | 12 | 13 | 14 | 15 |
| 38 | 16 | 17 | 18 | 19 | 20 | 21 | 22 |
| 39 | 23 | 24 | 25 | 26 | 27 | 28 | 29 |
| 40 | 30 |
- 3 Labor Day
The years 1962, 1973, 1979, 1990, 2007, 2018, 2029, 2035 have the same calendar as 2001: they start on the same weekday and are common years too, so September 11 is a Tuesday in each of them.
How to work out that September 11, 2001 was a Tuesday
Zeller's congruence gives the weekday of any Gregorian date with a few sums:
- Day q = 11; month m = 9.
- Year of the century K = 1; century J = 20.
- q + ⌊13 × (m + 1) ÷ 5⌋ + K + ⌊K ÷ 4⌋ + ⌊J ÷ 4⌋ + 5 × J = 11 + 26 + 1 + 0 + 5 + 100 = 143.
- 143 divided by 7 leaves 3, and 3 stands for Tuesday (0 is Saturday, 1 Sunday, up to 6 for Friday).
DateMath's calculator gets the same answer another way, by counting the days from a fixed date and taking the remainder after whole weeks.
What day of the week is September 11 in the coming years?
| Date | Weekday | Since 2001 |
|---|---|---|
| September 11, 2027 | Saturday | 26 years |
| September 11, 2028 | Monday | 27 years |
| September 11, 2029 | Tuesday | 28 years |
| September 11, 2030 | Wednesday | 29 years |
| September 11, 2031 | Thursday | 30 years |
| September 11, 2032 | Saturday | 31 years |
| September 11, 2033 | Sunday | 32 years |
| September 11, 2034 | Monday | 33 years |
| September 11, 2035 | Tuesday | 34 years |
| September 11, 2036 | Thursday | 35 years |
How DateMath finds the day of the week
DateMath counts the days from a fixed date to yours in the Gregorian calendar and takes the remainder after whole weeks, so every date in the years 1 to 9999 gets its weekday, leap days included. The same date is then numbered both ways: in the US, Sunday is day 1 of the week; in ISO 8601, Monday is day 1 and Sunday day 7. Today and tomorrow come from your device's date.
- The Gregorian calendar. DateMath treats every date as a Gregorian date, with its leap-year rule: a year divisible by 4 is a leap year, except century years not divisible by 400, so 2000 had a February 29 and 2100 will not. Source: Gregorian calendar.
- ISO 8601 week dates. DateMath numbers weeks by ISO 8601: weeks start on Monday, week 1 is the week with the year's first Thursday, and a year has 52 or 53 weeks. Source: ISO 8601.
DateMath's date math is tested against more than 100 cases worked out by hand. Every worked example and table on the site is computed with the same code the calculators run, so a page and its calculator can't disagree.
Frequently asked questions
- What day of the week was September 11, 2001 (9/11)?
- September 11, 2001 was a Tuesday. It was day 254 of 2001, in ISO week 37 and US week 37.
- What day of the week did 9/11 occur?
- On a Tuesday: September 11, 2001, the date written 9/11/01 in the US, was the second weekday of the week, a normal working and school day. The first plane struck the North Tower at 8:46 AM Eastern Time.
- What day of the week is September 11 this year?
- September 11 falls on a Friday in 2026 and on a Saturday in 2027. The table on this page gives the weekday of every anniversary for the next ten years.
- Was 2001 a leap year?
- No. 2001 had 365 days, so September 11, 2001 was day 254 of 365, with 111 days left in the year.