Shared custody on even / odd weeks: how it works

Alternating "one week each" is by far the most common shared custody arrangement. It works because both parents can check the same, unambiguous reference: the number of the week within the year.

How an even week is counted

Numbering follows the international ISO 8601 standard — the one used by calendars, payroll software and school timetables. Three rules are enough:

The week starts on Monday and ends on Sunday.
Week 1 of a year is the one containing the first Thursday of January.
A week whose number is divisible by two is even; otherwise it is odd.

One counter-intuitive consequence follows: a week belongs to the year of its Thursday. So 31 December regularly falls in week 1 of the following year, and 1 January in week 52 or 53 of the previous one.

The handover day

Nothing requires the children to change home on a Monday. Three options come up most often:

Friday evening, after school — the most frequent. The child spends the whole weekend with the parent taking that week.
Monday morning, at the start of the school day — custody weeks then match calendar weeks exactly.
Wednesday, often a short or free school day in France, splitting the week in two.

Whichever day is chosen, the parity is that of the week in which the period starts. A Friday handover in week 12 therefore opens the "week 12" period, even though most of its days fall in week 13. That is the reading used by parenting agreements, and by our schedule generator.

How the days actually split

Over an ordinary 52-week year, each parent gets exactly 26 weeks, or 182 days. Over a 53-week year, one of the two gets 27. That one-week gap usually evens out the following year, but it is better anticipated than discovered.

What belongs in the agreement

To avoid disputes, a parenting agreement is worth being specific on five points: the rhythm chosen and who takes the even weeks, the exact day and time of the handover, where it happens, how school holidays and public holidays are treated, and finally the rule that applies to 53-week years.

In case of disagreement, only the family court order or the approved agreement carries weight. The tools on this site help you picture a rhythm; they do not replace a legal document.