What week number is it right now?

The big number at the top of this page is the current week number, computed using ISO 8601 (Monday-start, the international standard). The page also shows the US Sunday-start equivalent and the simple ceil(day-of-year ÷ 7) variant. The number updates every 60 seconds and across day boundaries automatically.

How many weeks are in a year?

An ISO 8601 year has either 52 or 53 weeks. A common year is 52 weeks and 1 leftover day; a leap year is 52 weeks and 2 leftover days. A year reaches 53 weeks only when it starts on a Thursday, or when it is a leap year that starts on a Wednesday — about 71 of every 400 years. The simple ceil(day-of-year ÷ 7) numbering, by contrast, always produces 53 chunks because the last one is a partial week.

When does week 1 start?

Under ISO 8601, week 1 is the week containing the year's first Thursday — equivalently, the week containing January 4. Because weeks start on Monday, ISO week 1 can begin as early as December 29 of the previous year or as late as January 4. The US convention is different: week 1 runs from January 1 to the first Saturday, so it can be as short as one day.

What's the difference between ISO 8601 and US week numbers?

ISO 8601 weeks start on Monday, and week 1 is the week containing the year's first Thursday — so the first week always has at least four days in the new year. The US convention starts weeks on Sunday and treats the week containing January 1 as week 1, even if that week has only one day in the new year. Because US weeks start on Sunday, the two numbers differ every Sunday. In years where 1 January falls on a Friday or Saturday they differ on every day of the year. They disagree on 53 days in 2023, 52 days in 2026, every day of 2027 and every day of 2028.

Why do some years have 53 weeks?

A common year has 365 days, which is 52 weeks and 1 extra day. A leap year has 366, which is 52 weeks and 2 extra days. Whenever those extra days push the year's first or last week past the ISO four-day threshold, the year ends up with 53 ISO weeks instead of 52. It happens in roughly 71 of every 400 years (about every 5–6 years on average).

Can a date in early January belong to the previous year's week?

Yes — under ISO 8601. January 1, 2 or 3 sometimes falls in week 52 or 53 of the previous ISO week-year. For example, Friday January 1, 2027 is in ISO week 53 of 2026, because that week (Monday 28 December to Sunday 3 January) has its Thursday, 31 December, in 2026. Always pair an ISO week number with its ISO week-year to avoid ambiguity.

What week numbering does Excel use?

Excel's WEEKNUM function defaults to return type 1: Sunday-start, with January 1 always in week 1. That's the US convention shown on this page. Pass return_type 21 to WEEKNUM, or use ISOWEEKNUM, to get the ISO 8601 number instead.

Is the week number the same in every timezone?

It depends on the date you're computing for. Once you've fixed a calendar date (e.g. April 27 2026), the ISO and US week numbers are global — they're a property of the date itself, not the clock. But a single instant in UTC can be "today" in one timezone and "yesterday" in another, so the displayed week number on this page is computed against your local calendar day.

Week number

What week of the year is it?

Right now we're in ISO week 45 of 2026. Look up the week number for any date — ISO 8601, US (Sunday-start), or simple — and see the full 2026 week-by-week calendar. Week numbers are how Europe schedules sprints, how factories plan production runs, and how shipping carriers timestamp delivery windows. This page gives you the answer in every common system, refreshed live in your local timezone.

Right now (UTC)

Week 45 of 2026

Today is Thursday, Thu, Nov 5, 2026. That's ISO 8601 week numbering — the convention used by European business calendars and most of the world.

Week starts on

All three numbering systems for today

ISO 8601 (Mon-start)

Week 45

Mon, Nov 2, 2026 – Sun, Nov 8, 2026

ISO week-year 2026 · day 4 of 7

US (Sun-start)

Week 45

Sun, Nov 1, 2026 – Sat, Nov 7, 2026

Year 2026 · Jan 1 always in week 1

Simple (day ÷ 7)

Week 45

Independent of weekday — week 1 is Jan 1–7

Used by some manufacturing and ad-hoc schedules

Convert any date

Pick a date and see its week number in all three systems.

Date

ISO 8601

Week 45

Mon, Nov 2, 2026 – Sun, Nov 8, 2026

ISO week-year 2026 · Thursday

US (Sun-start)

Week 45

Sun, Nov 1, 2026 – Sat, Nov 7, 2026

Year 2026

Simple

Week 45

Day 309 of the year

ceil(day-of-year ÷ 7)

Year overview

All 53 ISO weeks of 2026

Mon–Sun ranges for every ISO 8601 week of the year. Useful for project planning, sprint cadence, and fiscal calendars. The current week is highlighted.

Week	Starts (Mon)	Ends (Sun)
Week 1	Dec 29	Jan 4
Week 2	Jan 5	Jan 11
Week 3	Jan 12	Jan 18
Week 4	Jan 19	Jan 25
Week 5	Jan 26	Feb 1
Week 6	Feb 2	Feb 8
Week 7	Feb 9	Feb 15
Week 8	Feb 16	Feb 22
Week 9	Feb 23	Mar 1
Week 10	Mar 2	Mar 8
Week 11	Mar 9	Mar 15
Week 12	Mar 16	Mar 22
Week 13	Mar 23	Mar 29
Week 14	Mar 30	Apr 5
Week 15	Apr 6	Apr 12
Week 16	Apr 13	Apr 19
Week 17	Apr 20	Apr 26
Week 18	Apr 27	May 3
Week 19	May 4	May 10
Week 20	May 11	May 17
Week 21	May 18	May 24
Week 22	May 25	May 31
Week 23	Jun 1	Jun 7
Week 24	Jun 8	Jun 14
Week 25	Jun 15	Jun 21
Week 26	Jun 22	Jun 28
Week 27	Jun 29	Jul 5
Week 28	Jul 6	Jul 12
Week 29	Jul 13	Jul 19
Week 30	Jul 20	Jul 26
Week 31	Jul 27	Aug 2
Week 32	Aug 3	Aug 9
Week 33	Aug 10	Aug 16
Week 34	Aug 17	Aug 23
Week 35	Aug 24	Aug 30
Week 36	Aug 31	Sep 6
Week 37	Sep 7	Sep 13
Week 38	Sep 14	Sep 20
Week 39	Sep 21	Sep 27
Week 40	Sep 28	Oct 4
Week 41	Oct 5	Oct 11
Week 42	Oct 12	Oct 18
Week 43	Oct 19	Oct 25
Week 44	Oct 26	Nov 1
Week 45now	Nov 2	Nov 8
Week 46	Nov 9	Nov 15
Week 47	Nov 16	Nov 22
Week 48	Nov 23	Nov 29
Week 49	Nov 30	Dec 6
Week 50	Dec 7	Dec 13
Week 51	Dec 14	Dec 20
Week 52	Dec 21	Dec 27
Week 53	Dec 28	Jan 3

ISO 8601 vs US week numbering — when each is used

The two dominant week-numbering systems disagree on two things: what day a week starts on, and what counts as “week one.” ISO 8601 — the international standard, defined formally in 1988 and revised in 2019 — runs weeks Monday through Sunday and treats week 1 as the week containing the year’s first Thursday. That rule guarantees every ISO week 1 has at least four days in the new calendar year, which keeps the “week of the year” intuition stable: the first full work week of January is always week 1 or 2.

The US convention starts weeks on Sunday and counts the week containing January 1 as week 1, no matter how short. That’s why a Saturday January 1 falls in “week 1” with only one US day before week 2 begins. This is the default in Excel’s WEEKNUM function, in Microsoft Outlook, in US-locale Apple Calendar, and in Google Sheets — so most American business workflows pick it up implicitly.

In practice, ISO is the safer choice for cross-border coordination. European firms in Germany, Sweden, the Netherlands, Norway, and Finland routinely refer to projects by ISO week number (“ship in week 18”), and shipping carriers, manufacturing schedules, and academic calendars in those countries operate the same way. US teams collaborating with European counterparts often run into off-by-one confusion, because the two numbers differ far more often than people expect: every Sunday, and in years that start on a Friday or Saturday (such as 2027 and 2028) on every single day.

Common business uses for week numbers

Fiscal calendars. Retailers using the National Retail Federation’s 4-5-4 calendar express every reporting period in “weeks,” and many companies also track work by ISO week. Sub-quarterly reporting often uses week numbers directly: “same-store sales for week 14” is unambiguous and easier to compare year-on-year than April 1–7.

Scrum sprints. Two- week sprints aligned to ISO weeks make planning trivial — sprint boundaries always fall on a Monday, and you can refer to the sprint by its starting week (“sprint 18–19”). Many engineering organizations adopt ISO weeks even in the US for this reason alone.

Manufacturing schedules. Auto parts, electronics, and pharmaceutical supply chains print “week 14 / 2026” on production run sheets and shipping pallets. The factory floor doesn’t need to know April 6 vs April 13 — it needs a unique 1-of-52 identifier that everyone in the chain agrees on. ISO is the global standard there.

Academic calendars. European universities frequently publish lecture schedules in ISO weeks: “the lab session is in weeks 5, 9 and 13.” That maps cleanly onto a 14-week semester and makes substituting a holiday week into a different week trivial.

The “first day of week” convention

Most of the world’s software defaults to one of three first-day-of-week conventions: Monday (ISO 8601, most of Europe, Australia), Sunday (United States, Canada, Japan, much of South Asia), and Saturday (parts of the Middle East and North Africa, where the work week starts on Sunday). The week-number system you choose is downstream of that convention — you can’t mix Monday-start weeks with US numbering, or you’ll end up with two-day weeks.

The toggle at the top of this page lets you pick which convention drives the “primary” week number shown in the hero. Your choice is saved locally in your browser, so the page remembers it the next time you visit.

Boundary reference

Week-number boundaries for 2026 and 2027

When ISO week 1 begins, when the final week ends, and which ISO week contains the first day of each quarter. Pair a week number with its ISO week-year — the two columns below can disagree by a few days.

Year	ISO weeks	Week 1 starts	Last week ends	Q2 / Q3 / Q4 week
2026	53long year	Dec 29, 2025	Jan 3, 2027	W14 / W27 / W40
2027	52	Jan 4, 2027	Jan 2, 2028	W13 / W26 / W39

Q1 begins in ISO week 1 only when 1 January falls on a Monday to Thursday; otherwise 1 January belongs to the last week (52 or 53) of the previous ISO week-year. January 1 2026 falls in ISO week 1 of week-year 2026.

ISO 8601 week numbering

How week numbers work

Week numbers look simple until two systems disagree. This section covers the ISO 8601 rules end to end: how week 1 is defined, why a year can have 53 weeks, and where the US convention differs.

The first-Thursday rule

ISO 8601 defines week 1 as the week containing the year’s first Thursday — equivalently, the week containing January 4, or the first week with the majority (four or more) of its days in the new year. This guarantees week 1 is never a tiny one-day stub, so “the first work week of January” is reliably week 1 or 2.

Weeks start on Monday

Every ISO 8601 week runs Monday through Sunday and has exactly seven days — there are no fractional weeks. A date’s ISO week is a property of the date itself, identical in every timezone once the calendar day is fixed.

Why some years have 53 weeks

A common year is 52 weeks plus one day; a leap year is 52 weeks plus two. A year reaches 53 ISO weeks only when January 1 is a Thursday, or a Wednesday in a leap year — 71 of every 400 years. The spacing is irregular: 2004 and 2009 were five years apart, 2009 and 2015 six, 2015 and 2020 five. 2026 is a 53-week year and 2027 is a 52-week year.

Week-year vs calendar-year

An ISO week belongs to exactly one ISO week-year, which can differ from the Gregorian year for a few days. January 1, 2026 falls in ISO week 1 of week-year 2026. Always pair a week number with its week-year, not the calendar year of the visible dates.

ISO vs US numbering

The US convention starts weeks on Sunday and treats the week containing January 1 as week 1, however short. ISO starts on Monday and uses the first-Thursday rule. The two often differ by a week: every Sunday, and in some years on every day (2027 and 2028, for example). Excel’s WEEKNUM defaults to the US rule; ISOWEEKNUM returns the ISO number.

The simple ceil(day ÷ 7) variant

Some manufacturing and ad-hoc schedules use the simplest rule of all: week N is days 7(N-1)+1 to 7N of the year. Week 1 is always January 1–7. This always yields 53 chunks because the last is a partial week, and it ignores weekday boundaries entirely.

Want the bigger picture? Year progress shows how much of the year has elapsed, and today’s date lists the day of the year and ISO week.

Week rules follow ISO 8601 (week dates); the US number follows the Excel WEEKNUM default (Sunday start, week 1 contains 1 January). Time zone and daylight-saving rules come from the IANA Time Zone Database, applied by your browser and our server. How we source and calculate times

Keep exploring

Other date and time tools you might want next.

Frequently asked

What week number is it right now?: The big number at the top of this page is the current week number, computed using ISO 8601 (Monday-start, the international standard). The page also shows the US Sunday-start equivalent and the simple ceil(day-of-year ÷ 7) variant. The number updates every 60 seconds and across day boundaries automatically.
How many weeks are in a year?: An ISO 8601 year has either 52 or 53 weeks. A common year is 52 weeks and 1 leftover day; a leap year is 52 weeks and 2 leftover days. A year reaches 53 weeks only when it starts on a Thursday, or when it is a leap year that starts on a Wednesday — about 71 of every 400 years. The simple ceil(day-of-year ÷ 7) numbering, by contrast, always produces 53 chunks because the last one is a partial week.
When does week 1 start?: Under ISO 8601, week 1 is the week containing the year's first Thursday — equivalently, the week containing January 4. Because weeks start on Monday, ISO week 1 can begin as early as December 29 of the previous year or as late as January 4. The US convention is different: week 1 runs from January 1 to the first Saturday, so it can be as short as one day.
What's the difference between ISO 8601 and US week numbers?: ISO 8601 weeks start on Monday, and week 1 is the week containing the year's first Thursday — so the first week always has at least four days in the new year. The US convention starts weeks on Sunday and treats the week containing January 1 as week 1, even if that week has only one day in the new year. Because US weeks start on Sunday, the two numbers differ every Sunday. In years where 1 January falls on a Friday or Saturday they differ on every day of the year. They disagree on 53 days in 2023, 52 days in 2026, every day of 2027 and every day of 2028.
Why do some years have 53 weeks?: A common year has 365 days, which is 52 weeks and 1 extra day. A leap year has 366, which is 52 weeks and 2 extra days. Whenever those extra days push the year's first or last week past the ISO four-day threshold, the year ends up with 53 ISO weeks instead of 52. It happens in roughly 71 of every 400 years (about every 5–6 years on average).
Can a date in early January belong to the previous year's week?: Yes — under ISO 8601. January 1, 2 or 3 sometimes falls in week 52 or 53 of the previous ISO week-year. For example, Friday January 1, 2027 is in ISO week 53 of 2026, because that week (Monday 28 December to Sunday 3 January) has its Thursday, 31 December, in 2026. Always pair an ISO week number with its ISO week-year to avoid ambiguity.
What week numbering does Excel use?: Excel's WEEKNUM function defaults to return type 1: Sunday-start, with January 1 always in week 1. That's the US convention shown on this page. Pass return_type 21 to WEEKNUM, or use ISOWEEKNUM, to get the ISO 8601 number instead.
Is the week number the same in every timezone?: It depends on the date you're computing for. Once you've fixed a calendar date (e.g. April 27 2026), the ISO and US week numbers are global — they're a property of the date itself, not the clock. But a single instant in UTC can be "today" in one timezone and "yesterday" in another, so the displayed week number on this page is computed against your local calendar day.