Week 1, 2026

ISO week 1 of 2026 (2026-W01) runs Monday, December 29, 2025 through Sunday, January 4, 2026. The full range is Dec 29 – Jan 4, 2026. Days follow the ISO Monday–Sunday convention. The US week label for dates in this window is 53–2. This spoke is the seven-day operations page for one week—not the 2026 matrix of all weeks, and not the hub that shows “today’s” US and ISO numbers side by side.

Federal holidays in this window: New Year's Day. ISO week 1 of 2026 begins on December 29, 2025 in the previous calendar year. When a holiday shifts observance to a nearby weekday, the table shows the date offices actually close rather than the statutory calendar date alone. The week number 1 does not increment or skip because a Monday is dark; only the working-day count inside Dec 29 – Jan 4, 2026 changes.

ISO versus US labels for this window

ISO weeks always start on Monday and end on Sunday. US week numbers on this site often follow a Sunday-start convention used in retail and broadcast schedules. Both labels appear here so a report that says 2026-W01 can be matched to a partner file that says US week 53–2. They can disagree, especially when Monday, December 29, 2025 or Sunday, January 4, 2026 sits in late December or early January.

If two teams merge timesheets this week, write both labels in the shared note for Dec 29 – Jan 4, 2026. Do not assume “week 1” is unambiguous. The ISO year inside 2026-W01 is the durable key; the civil year printed on a paycheck can differ on cross-year days. ISO week 1 of 2026 begins on December 29, 2025 in the previous calendar year.

Day-by-day breakdown

The grid lists all seven days with weekday names, calendar dates, and day-of-year numbers. That layout is for comparing ISO bounds against month-end billing cycles, school weeks that start on Sunday, or a pay period that ends on Thursday. Each row still belongs to 2026-W01 even if the month name changes mid-week. Payroll teams often map ISO weeks to pay periods even when checks are issued on a different weekday.

Download an ICS calendar file for this week to import the range into Outlook, Google Calendar, or Apple Calendar. The file contains one all-day event spanning Monday, December 29, 2025 through Sunday, January 4, 2026. It is a planning block, not a meeting invite: no clock times, no time zone conversion. After import, overlay actual meetings as separate timed events.

Holidays, capacity, and this week’s work

New Year's Day If the list is empty, treat Dec 29 – Jan 4, 2026 as a standard seven-day civil span and apply company holidays separately. If a federal observed day sits on Monday, shipping cutoffs that assume five full warehouse days will miss. Capacity planners should count the remaining weekdays after holidays, not divide the week’s volume by five by habit.

Confirm closures against 2026 US holidays when a customer SLA cites “next business day” inside this week. The spoke lists federal observed dates that fall in Dec 29 – Jan 4, 2026; it does not interpret a private employer’s floating holiday policy.

Stepping to adjacent weeks

Use previous week and next week to walk 2026 one ISO week at a time. Sprint reviews, incident windows, and production batches that are already numbered as consecutive weeks should move with those links rather than re-typing dates. Open the full 2026 week table when the next need is a jump to an arbitrary week number instead of a neighbor.

At year edges, previous or next may land in an adjacent ISO year. That is expected. 2026-W01 is still the title of this page; the neighbor page will carry its own label. Do not copy Monday, December 29, 2025 from this page onto a neighbor’s ticket.

Printable month context

When this week straddles two month names, a single ISO row is a poor poster. Download the 2026 yearly calendar for a sheet with all twelve months and week columns, or open a monthly calendar with larger day cells and highlight Monday, December 29, 2025 through Sunday, January 4, 2026 by hand. The spoke remains the source of the ISO bounds; the month sheet is the visual overlay.

Teachers and coaches who publish “week of” handouts should paste Dec 29 – Jan 4, 2026 in the header and keep weekday names in the body. Parents who think in Sunday-start weeks can read the US label 53–2 without converting the ISO title. Putting both on the handout prevents the Sunday-night email that asks whether Monday is in “this week.”

Tickets, cartons, and incident windows

A warehouse stamp that reads 2026-W01 is a claim about Dec 29 – Jan 4, 2026. Receiving should reject a pallet only after confirming both the ISO year inside the label and the Monday date Monday, December 29, 2025. A Jira fix version named “W1” should paste Dec 29 – Jan 4, 2026 in the description so support knows the deploy window. An incident postmortem that cites “week 1” should link this spoke so readers see the seven civil days, not a floating number.

If this week straddles a month-end close, finance still books by civil date; the ISO label is only the grouping key. Write 2026-W01 on the close checklist and keep invoice dates on the day rows. Mixing those two clocks is how a Thursday invoice lands in the wrong weekly dashboard.

What this week page is not

It is not a converter that turns an arbitrary week number into dates from a blank form—that is the week-dates tool. It is not a definition essay about why ISO exists; the hub covers the two standards in the large. It is the concrete span Dec 29 – Jan 4, 2026 for 2026-W01, with holidays, ICS, and neighbor links. Use it when a ticket, carton, or sprint already says week 1 and someone needs the seven civil days behind that stamp.