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Week number and day of year

Week number for any date: ISO 8601 week and week-numbering year, US week number, day of the year, days left in the year and the quarter.

अद्यतनित तपासलेली उदाहरणे: ५

= 2026-09-29
वापरून पाहा
ISO week
ISO week: 40
पूर्ण संख्या; जवळचे मूल्य; समान अंतरावर शून्यापासून दूर
ISO week-numbering year
2026
ISO week date
2026-W40-2
Day of the year
272
Days left in the year
93
Days in the year
365
Quarter
3
Weeks in that ISO year
53
US week number (Sunday start)
40
Year elapsed
74.5%

Tue 29 Sep 2026 is in ISO week 40 of 2026 (2026-W40-2), day 272 of 365 with 93 days left, in Q3.

2026 by quarter

Q1: 1 Jan 2026 to 1 Apr 2026Q1Q2: 1 Apr 2026 to 1 Jul 2026Q2Q3: 1 Jul 2026 to 1 Oct 2026Q3Q4: 1 Oct 2026 to 1 Jan 2027Q4Week 40Day 272 · Tue 29 Sep 2026
गणना कशी केली जाते S

  1. Weekday

    Tue 29 Sep 2026 is a Tuesday, ISO weekday 2 (Monday = 1).

  2. Find that week's Thursday

    ISO weeks run Monday to Sunday and belong to the year that contains their Thursday. This week's Thursday is Thu 1 Oct 2026, so the week-numbering year is 2026.

  3. आठवडा क्रमांक

    ⌊274−17⌋+1=40\left\lfloor \frac{274 - 1}{7} \right\rfloor + 1 = 40

    274 is the Thursday's day of the year.

  4. Day of the year

    N(date)−N(1 Jan)+1=272,365−272=93 days leftN(\text{date}) - N(\text{1 Jan}) + 1 = 272,\qquad 365 - 272 = 93\ \text{days left}

  5. US week number

    ⌊272−1+47⌋+1=40\left\lfloor \frac{272 - 1 + 4}{7} \right\rfloor + 1 = 40

    4 is 1 January's weekday counted from Sunday = 0; week 1 is the week containing 1 January.

Week number and day of year बद्दल

ISO 8601 weeks run from Monday to Sunday, and each week belongs to the year that contains its Thursday. Week 1 is therefore the week with the year's first Thursday, which is also the week containing 4 January. The calculator finds the Thursday of the date's week, takes its day of the year d, and computes ⌊(d − 1)/7⌋ + 1. It also gives the US-style number from Excel's WEEKNUM(date, 1), where weeks start on Sunday and week 1 is the week containing 1 January.

Week numbers appear in payroll periods, production plans and European business calendars. Near New Year the two systems part: 1 January 2027 is a Friday, so it falls in ISO week 53 of 2026 (2026-W53-5), while 30 December 2024 is already ISO week 1 of 2025 but US week 53 of 2024.

Day of the year counts 1 January as day 1, so 31 December is day 365, or 366 in a leap year.

सोडवलेली उदाहरणे

1 January 2026 (a Thursday)

Date
2026-01-01
ISO week
1
ISO week-numbering year
2026
ISO week date
2026-W01-4
Day of the year
1
Days left in the year
364
Quarter
1
US week number (Sunday start)
1

पडताळणीचा स्रोत: Python 3.8: date(2026,1,1).isocalendar() = (2026, 1, 4); tm_yday = 1

1 January 2027 belongs to week 53 of 2026

Date
2027-01-01
ISO week
53
ISO week-numbering year
2026
ISO week date
2026-W53-5
Day of the year
1
Weeks in that ISO year
53

पडताळणीचा स्रोत: Python 3.8: date(2027,1,1).isocalendar() = (2026, 53, 5)

30 December 2024 is in week 1 of 2025

Date
2024-12-30
ISO week
1
ISO week-numbering year
2025
Day of the year
365
Days left in the year
1
Quarter
4
US week number (Sunday start)
53

पडताळणीचा स्रोत: Python 3.8: date(2024,12,30).isocalendar() = (2025, 1, 1); tm_yday = 365 in a 366-day year

Last day of a leap year

Date
2024-12-31
Day of the year
366
Days left in the year
0
Days in the year
366
Year elapsed
100.0%

पडताळणीचा स्रोत: Python 3.8: date(2024,12,31).timetuple().tm_yday = 366

प्रश्न

How many weeks are there in a year?

52 or 53 ISO weeks. A year has 53 when it starts on a Thursday, or when it is a leap year starting on a Wednesday; that happens in 71 of every 400 years. 2020 and 2026 have 53 weeks, and the next are 2032 and 2037. 52 weeks cover only 364 days, so the spare day or two each year build up until a 53-week year absorbs them, usually 5 or 6 years apart.

Why do ISO and US week numbers differ?

They use different rules for the first week. ISO 8601 weeks start on Monday and week 1 contains the first Thursday of the year; Excel's ISOWEEKNUM follows this rule. The US convention, Excel's WEEKNUM with return type 1, starts weeks on Sunday and makes week 1 the week that contains 1 January, even if that week has only one day of the new year.

Can 1 January fall in week 52 or 53?

Yes, under ISO 8601 when 1 January is a Friday, Saturday or Sunday. 1 January 2027 is a Friday, so it belongs to week 53 of 2026 and ISO week 1 of 2027 starts on Monday 4 January. 1 January 2028 is a Saturday and falls in week 52 of 2027. In the other direction, 29 to 31 December can belong to week 1 of the next year.

Is the day of the year the same as the Julian date?

Only in informal use. In manufacturing and logistics a day-of-year code is often called a Julian date: 26 September 2026 is day 269, written 26269 in YYDDD form. Astronomers mean something else by Julian Day, a continuous count of days from 1 January 4713 BC in the Julian calendar; noon UTC on 26 September 2026 is Julian Day 2,461,310.

“Week number and day of year” किती अचूक आहे?

अचूकता तुमच्या इनपुटवर आणि पद्धतीच्या गृहीतकांवर अवलंबून असते. दशांश गणना 50 सार्थ अंक वापरते, पण अंदाज, संख्यात्मक पद्धती आणि मूळ डेटा कमी अचूक असू शकतात; दाखवलेल्या मूल्यांचे पूर्णांकन केल्याने या मर्यादा दूर होत नाहीत. स्वतंत्र स्रोतांतील सोडवलेल्या उदाहरणांशी पडताळणी: ५. उदाहरणार्थ, “1 January 2026 (a Thursday)” ची पडताळणी Python 3.8: date(2026,1,1).isocalendar() = (2026, 1, 4); tm_yday = 1 याच्याशी केली आहे.

या पद्धतीचा स्रोत कोणता?

ISO 8601-1:2019, §5.2.4 — week dates; Microsoft Excel ISOWEEKNUM and WEEKNUM functions.

या कॅल्क्युलेटरबद्दल

week=⌊day of year of that week’s Thursday−17⌋+1\text{week} = \left\lfloor \frac{\text{day of year of that week's Thursday} - 1}{7} \right\rfloor + 1

स्रोत

  1. ISO 8601-1:2019, §5.2.4 — week dates
  2. Microsoft Excel ISOWEEKNUM and WEEKNUM functions

संदर्भांशी पडताळलेले

या कॅल्क्युलेटरमध्ये स्वतंत्र स्रोतांमधील उत्तरांसह ५ सोडवलेली उदाहरणे आहेत. ती चाचणी संचात चालतात आणि तुम्ही ती येथेही चालवू शकता.

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