What does odd/even week custody mean?

It's a shared-custody arrangement where weekends (and sometimes the whole week) alternate between parents based on whether the current ISO calendar week number is odd or even, instead of a fixed 'every other Friday' rule that can drift.

How do I know if a week is odd or even?

Every week of the year has an ISO week number (week 1 through 52 or 53). If that number is odd, it's an odd week; if it's even, it's an even week. Most calendar apps and custody-tracking tools compute this automatically.

What happens at the start of a new year?

ISO week numbering resets in a way that doesn't always align with the calendar year boundary — the first few days of January can still belong to the last ISO week of the previous year. A schedule built on real ISO week numbers (not just 'week 1 of the year') handles this correctly without a manual adjustment.

What Is Odd/Even Week Custody Scheduling?

How does odd/even week custody work?

Odd/even week custody assigns weekends — or in some agreements, the entire week — to one parent during odd-numbered weeks of the year, and to the other parent during even-numbered weeks. It's one of the most common structures for shared physical custody because it's predictable, easy to verify independently, and doesn't require either parent to keep a private calendar to remember whose turn it is.

Why parents choose this structure

Compared to a rule like "every other Friday," which slowly drifts if a handover is ever missed or a holiday shifts things by a day, odd/even week scheduling is anchored to a number anyone can check: the ISO week number. Parent A always gets odd weeks, Parent B always gets even weeks — for the whole year, without needing to count forward from a start date.

A common pitfall: the year boundary

The ISO week numbering system doesn't reset cleanly on January 1st. The first Monday–Sunday block of a new year can actually still be counted as the final week of the previous year, or as week 1, depending on which day of the week January 1st falls on. Agreements that just say "week 1 is whoever had New Year's" instead of relying on the real ISO week number can end up ambiguous exactly when it matters most — around the holidays.

How weekday time is usually handled

Many agreements pair odd/even weekends with a separate, fixed weekday schedule (for example, one parent has Tuesday and Thursday every week, regardless of whose weekend it is), rather than flipping the entire week. The two rules — a fixed weekday pattern plus an alternating weekend — are tracked independently and then merged into one calendar.

Letting the calendar do the math

Manually tracking odd/even weeks, a separate weekday rule, and holiday exceptions on top of both is exactly the kind of bookkeeping that's easy to get wrong once, with real consequences. dayannu computes your actual custody calendar automatically from your agreement's rules — including odd/even weekend logic, fixed weekday exceptions, and holiday overrides — so neither parent has to do the arithmetic by hand.

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