Odd Week, Even Week Custody Schedule: the Calendar for 2026 and 2027
A week is even when its ISO week number is even, counting weeks from Monday to Sunday. The one time this trips parents up is this winter: week 53 of 2026 and week 1 of 2027 are both odd.
Published on August 9, 2026 · updated on October 1, 2026
Is this week even or odd?The week from Monday, September 28 to Sunday, October 4, 2026 is week 40. So it is an even week. Week 41 is odd, and the pattern carries on to the end of the year. Most of the time the answer really is that short. There is one exception, and it lands in the middle of winter.
How to tell whether a week is even or odd
Week numbers come from the ISO 8601 standard, the one used by most calendars, schools and businesses outside North America. Two rules cover it. A week runs from Monday to Sunday. Week 1 of a year is the week that contains the first Thursday of January.
That second rule means weeks can spill across the new year. Week 1 of 2026 began on Monday, December 29, 2025: it held Thursday, January 1, so the whole week counted as 2026.
Calendars set to start the week on Sunday, the usual default in the United States,
can show a different number for the same days. If your parenting plan says "even
weeks", it is worth checking once which numbering both of you use. In Google Sheets
or Excel, =ISOWEEKNUM(TODAY()) gives the ISO week number for today.
End of 2026: two odd weeks in a row
Most years have 52 ISO weeks. 2026 has 53, because January 1, 2026 fell on a Thursday. It only happens a few times a decade: 2020, 2026, then 2032 and 2037.
| Week | From Monday | To Sunday | Parity |
|---|---|---|---|
| 52 of 2026 | December 21, 2026 | December 27, 2026 | even |
| 53 of 2026 | December 28, 2026 | January 3, 2027 | odd |
| 1 of 2027 | January 4, 2027 | January 10, 2027 | odd |
| 2 of 2027 | January 11, 2027 | January 17, 2027 | even |
Read literally, "odd weeks with Mom" gives her the children from December 28 through January 10. That is fourteen nights in a row, and none for the other parent in that stretch.
Picture one family. Two kids, eight and ten. The agreement says even weeks with their father, odd weeks with their mother, switching on Friday after school, and a separate clause splits the winter break. If the break covers the last week of December, the holiday clause takes over and week 53 causes no trouble at all.
The surprise comes when school starts again. Week 1 of 2027 is odd, so the children go back to school from their mother's house. Their father has been counting "every other week" since September and expected his turn. Both parents are following a rule; they are just following different ones. That conversation goes badly on a Sunday night and much better in November.
What you can do
- Read the holiday clause first. If it covers the break, only the first school week of January is left to settle.
- Agree on a swap in writing, well before the holidays. A dated message that both of you keep is enough.
- Let the rule run and note that the extra week will even out later. That works, as long as you both decide it ahead of time.
Even and odd weeks in 2027
2027 has 52 weeks, so the change to 2028 is ordinary: week 52, even, is followed by week 1 of 2028, odd.
| Week | From Monday | To Sunday | Parity |
|---|---|---|---|
| 1 of 2027 | January 4, 2027 | January 10, 2027 | odd |
| 52 of 2027 | December 27, 2027 | January 2, 2028 | even |
| 1 of 2028 | January 3, 2028 | January 9, 2028 | odd |
One detail matters for the first weekend of the year. January 2 and 3, 2027 still belong to week 53 of 2026, so that weekend is odd. A printed calendar that labels it "week 1" is wrong, and that is the first thing to check before trusting one. If your schedule counts weekends rather than weeks, the details are in our guide to even and odd weekends.
The handover day matters as much as the week
ISO weeks start on Monday, but children rarely switch homes on a Monday. Two patterns cover most schedules: Friday after school to the next Friday, or Sunday evening to Sunday evening.
With a Friday handover, the "even week" really begins on the Friday of the odd week, three days before its Monday. A lot of arguments start in that gap. One sentence written down once prevents them: "the children arrive at Dad's on the Friday before each even week."
When the order doesn't say who has even weeks
Some orders only say "alternating weeks". Then the date of the first handover sets everything that follows. Write it down that day, along with the parity of that week: three years on, nobody remembers it for sure.
Neither parent is entitled to even weeks by default. Over a year the two halves come out about the same, and school breaks are usually handled by their own clause, as explained in how to share school holidays and Christmas.
Keeping one calendar for two homes
A paper chart works for a few months. After that, holidays, one-off swaps and weeks like week 53 get written down on one side only, and nobody can say how many nights each parent actually had.
In Nestido, you describe your schedule once and the calendar fills in the months ahead. A one-off swap sits on top of it without undoing the rest, and once you invite the other parent, you both look at the same calendar. If you are still choosing a pattern, compare them in 50/50 custody schedule examples.