Even or Odd Weekend: How to Tell Which One Is Yours, and the January 2027 Trap
A weekend takes the parity of its week: Saturday and Sunday both belong to the week that started the Monday before. Here's how to check it in thirty seconds, why two parents looking at their own calendars can land on different answers, and why January 2027 has two odd weekends in a row.
Published on August 26, 2026
"Every other weekend," the agreement says. The question is which ones. The answer fits in one sentence: a weekend takes the parity of its week, because Saturday and Sunday both belong to the week that started the Monday before. An even weekend is one that falls in an even week, an odd weekend one that falls in an odd week, and there's no edge case.
That doesn't stop two parents acting in good faith from reading two different numbers for the same Saturday. Here's why, and what to check before January 2027, when the alternation breaks.
The rule that decides, and it isn't up for debate
A week's number comes from a standard, ISO 8601, the one used by employers, schools and digital calendars. Two rules are enough to rebuild the whole thing.
- A week starts on Monday and ends on Sunday.
- Week 1 of a year is the one containing its first Thursday, in other words the one with at least four days of the new year in it.
The first rule is all you need for a weekend: Saturday and Sunday fall in the same week, the one that's ending. The weekend of June 12 and 13, 2027, for instance, falls in week 23: it's an odd weekend, from Saturday morning through Sunday night, with no half of it changing sides.
In a spreadsheet: =ISOWEEKNUM(TODAY()). On a phone, week
numbers aren't shown by default: in Google Calendar the option is under
display settings, on an iPhone it's in Settings, then Calendar.
Why two calendars don't give the same number
This is where almost every disagreement starts, and it isn't the standard that's inconsistent: it's that not everyone follows the same one. Part of the world starts its week on Sunday, and many apps, spreadsheets and printed calendars default to that convention.
In a calendar that starts on Sunday, a weekend's Sunday leaves its own week and joins the next one. The same weekend then ends up split across two numbers, and two parents each checking their own app read two different answers for the same Saturday. The disagreement isn't about the parity, it's about the setting.
Before any discussion, then, it's worth checking that both calendars display weeks running Monday through Sunday. That's where nearly every week-number mix-up gets resolved.
"Every other weekend" doesn't say which ones
An agreement can simply say "every other weekend" without specifying even or odd. In that case, the date of the first weekend spent with one parent sets the pattern for everything after, and it's worth writing it down the day it happens: three years later, nobody remembers it with certainty.
One thing that comes up often: "even weekends for dad" isn't a rule or a convention. Both halves are strictly equivalent, and over a year they split long weekends and holidays roughly evenly.
The trap: January 2027 has two odd weekends in a row
An ISO year has 52 weeks, except when it has 53. That's the case for 2026, whose January 1 falls on a Thursday; 2027 has 52. That extra week doesn't show up anywhere during the year, and gets paid for all at once at the turn of 2027.
| Weekend | Week | Parity |
|---|---|---|
| December 26 and 27, 2026 | 52 of 2026 | even |
| January 2 and 3, 2027 | 53 of 2026 | odd |
| January 9 and 10, 2027 | 1 of 2027 | odd |
| January 16 and 17, 2027 | 2 of 2027 | even |
The weekend of January 2 and 3, 2027 isn't in week 1 of 2027: it still belongs to week 53 of 2026. Two odd weekends follow one another, and the parent with the even weekends goes three weeks without one, from December 27, 2026 to January 16, 2027. It isn't a mistake, it's the alternation playing out exactly as written.
The same thing happened at the end of 2020 and will happen again at the end of 2032. It always lands in the same spot on the calendar: the year-end holidays, the very period many agreements carve out a separate split for.
What you can do, in order
- Check what the agreement says about the year-end holidays. When it spells out a separate split for that period, that split usually overrides the weekend alternation, and the question resolves itself. That's the first thing to check, before any discussion.
- Agree on an extra swap, in writing, back in November rather than at the last minute. A dated message both parents can look back at is enough.
- Leave it as is, and note that the gap will even out later. That's a perfectly valid answer, as long as it's a choice and not something that just happens.
Counting weekends doesn't tell you how much time each parent actually had
Two parents alternating weekends almost never end up with the same number of nights anyway: a weekend sometimes starts Friday night and sometimes Saturday morning, school holidays don't follow the alternation, and a one-off swap rarely gets logged on both sides. The only unit that counts without argument is the night.
That's exactly what Nestido does: you set your custody rhythm once, the app fills in the months ahead, weekends included, and you only log the exceptions. Week numbers, 2026's 53 weeks and school holidays are all built in, and the other parent sees the same calendar at the same time.
To go further: even or odd week, the full rule, which custody schedule to choose and counting nights without arguing.