Custody time calculator

Why a custody time calculator matters

When two households share the care of a child, two questions come up early and often. How is the time split, and what does that mean across a year. People reach for these numbers for honest reasons. Planning the school week. Drafting a parenting plan. Understanding the bands the Child Maintenance Service uses. Working out who is paying for what at which point in the month.

Most UK co-parenting families settle into a rota that repeats every fortnight. A 14-day window catches the common patterns without forcing anyone into an artificial monthly view. Week-on-week-off. School week with one parent and weekends with the other. Alternating weekends. The 2-2-3 split that many separated families use when both parents live close to school. Each pattern produces a different annual nights figure, and a different sense of whose week is whose.

This calculator does one job. It turns a 14-day pattern into clear numbers and a shareable link. It does not tell you which pattern is right for your family. It does not tell you what a court will order. It is a quiet planning aid you can hand to your solicitor, your mediator, or the other parent, with the maths already done.

How to use it in five steps

1. Pick the pattern that most closely matches your week. The dropdown covers the four most common UK arrangements.
2. Adjust any individual day on the 14-day grid. Tap a day to cycle through Parent A, Parent B and Shared.
3. Rename the parent labels if it helps the conversation. Many families use first names or "Mum's house" and "Dad's house".
4. Read the per-fortnight and annual projection. Both update live as you change the pattern.
5. Copy the share link or export a PDF. The link contains your full pattern. The PDF is one page, ready to attach to a parenting plan.

How shared days are counted

A "shared" day in this calculator is treated as half a night to each household. This is a planning approximation. In real arrangements the time on a shared day is shaped by the handover hour, the school pickup, and the child's bedtime. If you need a more precise split, set the day to whichever parent has the bedtime and use the notes feature in your parenting plan to record the daytime arrangement.

The Child Maintenance Service uses bands measured in nights of shared care per year. The thresholds are 52, 104, 156 and 175 nights, with maintenance reduced as the band rises. The annual nights figure on this page is a useful first estimate. It is not a CMS calculation, and it cannot account for school holidays, illness, or one-off changes. If maintenance bands matter to you, confirm the figures with CMS or a family law professional before relying on them.

When the maths is not the point

Family time is not really a percentage. A 60-40 split with the school week in one home and four nights in the other can feel very different from a 60-40 split where one household has every weekend. The numbers help structure a conversation. They do not replace the conversation.

Most parenting plans that work over time share a few traits. They are written down. They name the regular pattern, the holiday pattern, and the rule for when one parent needs to swap a day. They include a way to log handovers and decisions, so neither parent has to remember every detail from memory. They are reviewed at least once a year.

Haevn was built around that observation. The calculator on this page is the first piece. The rest of the app gives you a shared family calendar, an append-only family chat, a custody handover log, and a decision log, all with the same privacy posture as this page. Your family's data is not used to train AI models or build advertising profiles.

Privacy of this tool, in plain English

Everything you type stays on your device. The calculation runs in your browser. The only place your inputs go is the URL of this page, so you can copy a link and share the same view with another parent or your solicitor. We do not log the contents of your URL. We do not store your custody pattern, your parent labels, or your annual nights figure. There is no server call when you change a day, copy the link, or download the PDF.

Common questions

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