# WeekIsIt — ISO 8601 Week Numbers & Calendar Tools

> WeekIsIt.com answers "what week is it?" It shows today's ISO 8601 week number and provides free, server-rendered tools: full year calendars, date-to-week conversion, a weekday finder, a pregnancy week calculator, fiscal-calendar week numbering, and "when is [holiday]" pages with the next date and live countdowns for dozens of events. No login, no paywall, no JavaScript required for core features.

## Live data (generated 2026-07-22)
- Current ISO week: week 30 of 2026
- Week range: 2026-07-20 to 2026-07-26 (Monday to Sunday)
- US week number (Sunday start): 30
- Day 203 of 365 — 162 days remaining in 2026
- 23 weeks remaining — currently in quarter Q3
- 2026 has 53 ISO weeks in total

## How ISO 8601 week numbers work
ISO 8601 weeks start on Monday. Week 1 is the week containing the year's first Thursday — equivalently, the week containing January 4. Because of this rule a year has either 52 or 53 ISO weeks, and dates in early January or late December can belong to the neighbouring year's week numbering. 2026 has 53 weeks. This differs from the common US convention, where weeks start on Sunday and week 1 is the week containing January 1.

## Core tools
- [Current week number](https://weekisit.com/): the live ISO week number for today, updated automatically each week
- [Week calculator](https://weekisit.com/week-calculator): convert any calendar date to its ISO week number, and convert any week number back to its date range
- [Weekday calculator](https://weekisit.com/weekday-calculator): find which day of the week any past or future date falls on
- [Pregnancy week calculator](https://weekisit.com/pregnancy-week): current pregnancy week, trimester and estimated due date from the last period or conception date
- [Fiscal calendar](https://weekisit.com/fiscal-calendar): fiscal-year week numbering for US (October start) and UK (April start) accounting calendars
- [2026 week calendar](https://weekisit.com/week-numbers-2026): every ISO week of 2026 with its Monday-to-Sunday date range (other years work too, e.g. /week-numbers-2027)

## Reference guides
- [ISO week number explained](https://weekisit.com/iso-week-number): the ISO 8601 week-numbering standard in plain language
- [How many weeks are in a year](https://weekisit.com/weeks-in-a-year): why most years have 52 weeks and some have 53
- [Blog](https://weekisit.com/blog): articles on week numbering, calendars and date calculations

## When is...? — holiday & event dates
Every event below has a dedicated page at /when-is-[event] with its full history, traditions, regional variations and FAQs. Dates shown are the next upcoming occurrence as of 2026-07-22.
### Major US holidays
- [When is New Year's Day](https://weekisit.com/when-is-new-years-day): next Fri, Jan 1, 2027. The first day of the calendar year and a public holiday across most of the world. It marks fresh starts, resolutions and the end of the holiday season.
- [When is Martin Luther King Jr. Day](https://weekisit.com/when-is-martin-luther-king-day): next Mon, Jan 18, 2027. A US federal holiday honouring the civil rights leader Dr. Martin Luther King Jr. It's marked by service projects and remembrance.
- [When is Presidents' Day](https://weekisit.com/when-is-presidents-day): next Mon, Feb 15, 2027. A US federal holiday honouring American presidents, originally George Washington's birthday. The long weekend is famous for retail sales.
- [When is Memorial Day](https://weekisit.com/when-is-memorial-day): next Mon, May 31, 2027. A US federal holiday honouring military personnel who died in service. It's widely seen as the unofficial start of summer.
- [When is Juneteenth](https://weekisit.com/when-is-juneteenth): next Sat, Jun 19, 2027. Juneteenth marks the end of slavery in the United States, commemorating June 19, 1865. It became a federal holiday in 2021.
- [When is Independence Day](https://weekisit.com/when-is-independence-day): next Sun, Jul 4, 2027. The Fourth of July celebrates the US Declaration of Independence in 1776, with fireworks, parades and cookouts nationwide.
- [When is Labor Day](https://weekisit.com/when-is-labor-day): next Mon, Sep 7, 2026. A US federal holiday honouring the labour movement and workers. It marks the unofficial end of summer.
- [When is Columbus Day](https://weekisit.com/when-is-columbus-day): next Mon, Oct 12, 2026. A US federal holiday marking Columbus's 1492 arrival in the Americas. Many places now observe Indigenous Peoples' Day on the same date.
- [When is Veterans Day](https://weekisit.com/when-is-veterans-day): next Wed, Nov 11, 2026. A US federal holiday honouring all military veterans, held on the anniversary of the end of World War I.
- [When is Thanksgiving](https://weekisit.com/when-is-thanksgiving): next Thu, Nov 26, 2026. A US holiday of gratitude centred on a family feast with turkey. It kicks off the holiday shopping season.
- [When is Christmas Day](https://weekisit.com/when-is-christmas): next Fri, Dec 25, 2026. Christmas celebrates the birth of Jesus and is one of the most widely observed holidays worldwide, religious and secular alike.

### Observances & special days
- [When is Valentine's Day](https://weekisit.com/when-is-valentines-day): next Sun, Feb 14, 2027. A day for romance and affection, marked with cards, flowers and gifts between partners and loved ones.
- [When is Super Bowl Sunday](https://weekisit.com/when-is-super-bowl): next Sun, Feb 14, 2027. The championship game of the NFL and the most-watched US TV broadcast of the year, famous for its ads and halftime show.
- [When is St. Patrick's Day](https://weekisit.com/when-is-st-patricks-day): next Wed, Mar 17, 2027. A celebration of Irish culture and the patron saint of Ireland, marked by parades and the colour green worldwide.
- [When is April Fools' Day](https://weekisit.com/when-is-april-fools-day): next Thu, Apr 1, 2027. A day for harmless pranks and hoaxes. Brands and media often join in with playful fake announcements.
- [When is Earth Day](https://weekisit.com/when-is-earth-day): next Thu, Apr 22, 2027. A global day of environmental awareness and action, first held in 1970.
- [When is Cinco de Mayo](https://weekisit.com/when-is-cinco-de-mayo): next Wed, May 5, 2027. Marks the Mexican army's 1862 victory at the Battle of Puebla. In the US it's a celebration of Mexican-American culture.
- [When is Mother's Day](https://weekisit.com/when-is-mothers-day): next Sun, May 9, 2027. A day honouring mothers and motherhood, celebrated with cards, flowers and family gatherings.
- [When is Father's Day](https://weekisit.com/when-is-fathers-day): next Sun, Jun 20, 2027. A day honouring fathers and father figures, often marked with gifts and shared meals.
- [When is Halloween](https://weekisit.com/when-is-halloween): next Sat, Oct 31, 2026. An evening of costumes, trick-or-treating and spooky fun, rooted in old harvest and All Hallows' Eve traditions.
- [When is Black Friday](https://weekisit.com/when-is-black-friday): next Fri, Nov 27, 2026. The shopping day after Thanksgiving, known for steep discounts and the unofficial start of holiday shopping.
- [When is Cyber Monday](https://weekisit.com/when-is-cyber-monday): next Mon, Nov 30, 2026. The Monday after Thanksgiving, focused on online deals. It complements Black Friday's in-store sales.
- [When is New Year's Eve](https://weekisit.com/when-is-new-years-eve): next Thu, Dec 31, 2026. The last day of the year, celebrated with parties, fireworks and the midnight countdown.

### Easter & the Christian calendar
- [When is Mardi Gras (Fat Tuesday)](https://weekisit.com/when-is-mardi-gras): next Tue, Feb 9, 2027. The final day of feasting before Lent, famous for carnival celebrations in New Orleans and around the world.
- [When is Ash Wednesday](https://weekisit.com/when-is-ash-wednesday): next Wed, Feb 10, 2027. The first day of Lent in Western Christianity, a season of reflection leading to Easter.
- [When is Palm Sunday](https://weekisit.com/when-is-palm-sunday): next Sun, Mar 21, 2027. The Sunday before Easter, marking Jesus's entry into Jerusalem and the start of Holy Week.
- [When is Good Friday](https://weekisit.com/when-is-good-friday): next Fri, Mar 26, 2027. Commemorates the crucifixion of Jesus. It's a public holiday in many countries.
- [When is Easter Sunday](https://weekisit.com/when-is-easter): next Sun, Mar 28, 2027. The central feast of the Christian year, celebrating the resurrection of Jesus. Its date drives many other observances.
- [When is Easter Monday](https://weekisit.com/when-is-easter-monday): next Mon, Mar 29, 2027. The day after Easter Sunday, a public holiday in many countries including the UK, Canada and Australia.
- [When is Pentecost](https://weekisit.com/when-is-pentecost): next Sun, May 16, 2027. Celebrates the descent of the Holy Spirit, 50 days after Easter. Also called Whitsunday.

### Seasons & solstices
- [When is Spring Equinox](https://weekisit.com/when-is-spring-equinox): next Sat, Mar 20, 2027. The start of astronomical spring in the Northern Hemisphere, when day and night are nearly equal.
- [When is Summer Solstice](https://weekisit.com/when-is-summer-solstice): next Mon, Jun 21, 2027. The longest day of the year in the Northern Hemisphere and the start of astronomical summer.
- [When is Autumn Equinox](https://weekisit.com/when-is-autumn-equinox): next Tue, Sep 22, 2026. The start of astronomical autumn in the Northern Hemisphere, with day and night nearly equal.
- [When is Winter Solstice](https://weekisit.com/when-is-winter-solstice): next Mon, Dec 21, 2026. The shortest day of the year in the Northern Hemisphere and the start of astronomical winter.

### Daylight saving (US clock changes)
- [When is Daylight Saving Time starts](https://weekisit.com/when-is-daylight-saving-time-starts): next Sun, Mar 14, 2027. Clocks spring forward one hour, shifting daylight into the evening. You lose an hour of sleep.
- [When is Daylight Saving Time ends](https://weekisit.com/when-is-daylight-saving-time-ends): next Sun, Nov 1, 2026. Clocks fall back one hour, returning to standard time. You gain an hour of sleep.

## Blog articles
- [World Cup 2026 Calendar: All 104 Games, Dates and .ics](https://weekisit.com/blog/world-cup-2026-calendar-all-104-games): World Cup 2026 calendar with all 104 games, flags, dates and kickoff times. Download the full schedule as an .ics and add it to Apple, Google or Outlook.
- [Week Number API: Free ISO 8601 REST Endpoint (2026)](https://weekisit.com/blog/week-number-api-free-iso-8601-rest-endpoint): Week Number API: a free REST endpoint that returns the ISO 8601 week number for any date. No key, CORS enabled, with JS, curl and Python examples.
- [What Quarter Is It Now? Q1, Q2, Q3, Q4 Dates for 2026](https://weekisit.com/blog/what-quarter-is-it-now): What quarter is it? Right now it's Q2 2026, running April 1 to June 30. See exact Q1, Q2, Q3 and Q4 dates for 2026, plus how fiscal quarters differ.
- [Zero Waste Week 2026: Dates, ISO Week and How to Join](https://weekisit.com/blog/zero-waste-week-2026): Zero Waste Week 2026 runs Monday September 7 to Sunday September 13, the first full week of the month (ISO week 37). Here are the dates and how to take part.
- [How Many Work Weeks Are in a Year? (2026 Business Guide)](https://weekisit.com/blog/how-many-work-weeks-are-in-a-year): Work weeks in a year come to about 52, or 261 weekdays in 2026. See working day totals for the US, UK, Canada and Australia for payroll and project planning.
- [Calculate Week Numbers in Excel, Sheets & Python (2026)](https://weekisit.com/blog/calculate-week-numbers-in-excel-sheets-and-python): Calculate the week number in Excel, Google Sheets, and Python with ISOWEEKNUM, WEEKNUM, and isocalendar(). Copy-paste formulas, plus why ISO and default differ.
- [Week numbers 2026: complete calendar of all 53 weeks](https://weekisit.com/blog/week-numbers-2026-complete-calendar-of-all-53-weeks): Week numbers 2026 in one place: the full ISO 8601 calendar of all 53 weeks, with exact Monday-to-Sunday dates for every week. Free and printable.
- [US vs ISO Week Numbers: Difference & Which to Use (2026)](https://weekisit.com/blog/us-vs-iso-week-numbers-difference-and-which-to-use): US vs ISO week numbers, compared: ISO weeks start Monday with a first-Thursday rule; US weeks start Sunday and put January 1 in week 1. Which to use.
- [What Week Does the Third Trimester Start? (Week 28)](https://weekisit.com/blog/what-week-does-the-third-trimester-start): The third trimester starts at week 28 of pregnancy and runs to week 40 or birth. Get the full trimester-by-week breakdown, real dates, and a quick FAQ.
- [How many weeks are in a year? (2025 and 2026 explained)](https://weekisit.com/blog/how-many-weeks-are-in-a-year): How many weeks are in a year? Every calendar year has 52 weeks plus 1 or 2 extra days, but in ISO 8601 some years, like 2026, have a full 53 weeks.
- [ISO 8601 week numbers explained: why January can be week 53](https://weekisit.com/blog/iso-8601-week-numbers-explained): ISO 8601 week numbers run Monday to Sunday, so the start of January can fall in week 52 or 53 of the year before. Here's exactly why, with real dates.

## Regional versions
Prefix most URLs with a country code for localised holidays and week conventions: /us/, /uk/, /ca/, /au/. Example: https://weekisit.com/uk/ shows UK week numbering and bank holidays.

## API
- [JSON API](https://weekisit.com/api/week): GET https://weekisit.com/api/week returns the current week, year, start, end, day_of_year, days_remaining, quarter and total_weeks as JSON. No API key, CORS enabled, 60-second cache.
- [API documentation](https://weekisit.com/api): endpoint details and example responses

## Optional
- [Sitemap](https://weekisit.com/sitemap.xml): complete list of indexed pages
- Data on WeekIsIt is free to use and reference; no attribution required.