Co-Parenting Custody Calendar

A custody schedule is a 52-weeks-a-year logistical contract executed by two people who may barely speak. Most parenting plans die not on big legal questions but on calendar mechanics: whose Friday does the exchange happen, who gets spring break in even years, does a 2-week vacation create a 9-day gap for the other parent, and whether the split is actually 50/50 or quietly 42/58. This skill turns plan language into dated reality — and reality back into evidence.

When to Use

• Drafting a parenting plan: choosing between alternating weeks, 2-2-3, 3-4-4-3 — and seeing the actual overnight counts, not the brochure math
• Mediation or court prep: an honest audit of what a proposed schedule really gives each parent (overnights, weekends, longest gap)
• Holiday season planning: who has first pick this year, what the alternating-priority table says for the next 12 months
• One parent travels / deployment / work shift changes: patch the rotation and handle make-up time fairly
• Dispute about missed exchanges: a dated log with makeup-time doctrine
• Rebuilding after "we just sort of drifted" into an informal schedule

Don't use for: situations involving abuse, abduction risk, or urgent child-safety concerns — those need a lawyer and possibly emergency orders immediately, not calendar tooling. International parental abduction risk (Hague Convention cases) is also out of scope.

The Method

1. plan — generate the dated rotation from a block-boundary start date. Print run-by-run (which parent, from when to when), overnight counts and percentages, exchanges per month. --ics exports an all-day custody calendar plus exchange events with a 12-hour pack reminder.
2. holidays — the year's holiday table. Alternating priority (odd/even years flip first pick) with Mother's/Father's Day pinned to the named parent and the child's birthday as a listed holiday. Includes the plan-wording fix that kills edge disputes (6pm prior day / 8am next day).
3. fairness — audit any rotation over any period: overnights, percent, weekend days, longest gap without an overnight. Flags < 35% (the common US shared-custody threshold; below it, child support formulas and "custodial parent" designations shift).
4. override — patch a date range to one parent with the make-up-time rule: equal-length block offered in writing within 30 days, and a ready log entry. This is the single biggest source of quiet drift.

# See what 2-2-3 actually looks like for the next 4 weeks
python3 scripts/co_parenting_calendar.py plan --schedule 2-2-3 \
    --start 2026-11-02 --days 28 --label-a "Alex" --label-b "Sam"

# Full-year audit of alternating weeks
python3 scripts/co_parenting_calendar.py fairness --schedule alternating-week \
    --start 2026-01-01 --end 2026-12-31

# Holiday table for 2027, Sam first pick in odd years
python3 scripts/co_parenting_calendar.py holidays --year 2027 --odd B \
    --mother A --father B --birthday 2019-05-14

# Patch a trip + make-up doctrine
python3 scripts/co_parenting_calendar.py override --from 2027-03-30 \
    --to 2027-04-10 --parent A --reason "work trip"

Rotation Cheat Sheet

Common Pitfalls

1. Starting the rotation on a non-boundary date. --start must be a block boundary (Monday for week-based patterns); otherwise every printed block is shifted and the ICS lies.
2. Trusting "50/50" marketing. Alternating weeks over a school year is 50/50 only if holidays and summer are separately split — run fairness on the plan-as-written, not the label.
3. Ignoring the longest-gap stat. A vacation override can create a 14+ day gap for a young child. Check fairness after every override.
4. Holidays by date, not by rule. "Thanksgiving with Mom" without an odd/even rule guarantees a 2027 fight. The holidays table alternates priority yearly and pins Mother's/Father's Day.
5. No exchange-time wording. Plans that say "exchange Friday" without a time produce parking-lot standoffs. Write 6pm/8am windows.
6. Treating makeup time as optional. The make-up rule (equal block, written offer within 30 days) is what keeps a one-off override from becoming the new normal.
7. Using this output as legal advice. It's a calculator and wording aid. State law varies (thresholds, holiday definitions); a family-law attorney should review anything filed with a court.

Verification Checklist

• Start date is a block boundary (Mon for week-based schedules)
• Overnight percentages match expectations of both parents
• Longest-gap checked after adding any override
• Holiday table shows odd/even alternation and pinned days
• ICS imports into Google/Apple calendar with exchange times
• Make-up offers documented in writing when overrides happen

References

• references/parenting-plan-clauses.md — clause library for exchanges, holidays, make-up time, right-of-first-refusal, communication protocols (parenting apps), and the dispute ladder short of court.