How Custody Percentages Are Calculated
Courts determine custody percentages by counting overnights per year for each parent. The formula is straightforward: divide one parent's overnights by 365. A parent with 182 overnights has 49.9% — effectively a 50/50 split. A parent with 73 overnights has 20%.
Some states count “hours of care” instead of overnights, but the overnight method is the standard in the vast majority of US jurisdictions. The distinction matters because daytime visits without an overnight may not count toward custody percentage in states that use the overnight standard.
Our calculator uses the overnight method. Enter your schedule type or a custom overnight count, and it divides by 365 to produce the percentage split.
Common Custody Schedules Compared
Here are the most common custody arrangements, ranked from least to most time with the non-custodial parent:
| Schedule | Overnights (P2) | Percentage | Typical Arrangement |
|---|---|---|---|
| Every Other Weekend | 52 | 86/14 | 26 weekends × 2 nights; no weekday time |
| 80/20 | 73 | 80/20 | Every other weekend + one weeknight |
| 70/30 | 110 | 70/30 | Every other weekend + two weeknights |
| 60/40 | 146 | 60/40 | Alternating weeks with extra days; or 4-3 schedule |
| Equal 50/50 | 182 | 50/50 | Alternating weeks, 2-2-3 rotation, or 3-4-4-3 |
The “Parent 2 overnights” column shows how many nights the non-custodial parent (or the parent with less time) has under each schedule. Parent 1 gets the remaining 365 minus that number.
How Parenting Time Affects Child Support
In most US states, more parenting time reduces child support payments. The logic: a parent spending more overnights with the child incurs more direct expenses (food, utilities, activities), so the cash transfer between households decreases.
The threshold where parenting time starts affecting the calculation varies by state. Some states adjust at 20% time, others at 30% or 40%. A few states — like Michigan and Ohio — have a sliding scale that starts adjusting from the first overnight. Equal 50/50 custody does not automatically mean zero child support; the higher earner typically still pays something to equalize the child's standard of living between households.
Use this calculator to determine your custody percentage, then plug that number into your state's child support formula or worksheet.
Tips for Negotiating a Custody Schedule
- Start with the child's routine. School schedule, extracurricular activities, and the child's age should drive the arrangement — not what the parents prefer. Young children (under 3) generally do better with shorter, more frequent transitions.
- Proximity matters. 50/50 schedules work best when both parents live within the same school district. Long commutes between homes create stress and logistical nightmares for everyone.
- Build in flexibility. A rigid schedule that looks fair on paper breaks down during holidays, sick days, and school vacations. Include a process for swapping days and handling exceptions.
- Use a parenting app. OurFamilyWizard, TalkingParents, or AppClose create documented communication trails. Courts increasingly require them in contested custody cases.
- Show the math. Use this calculator so both parents see the same overnight counts and percentages. Numbers reduce arguments.
- Revisit annually. What works for a 3-year-old may not work for a 12-year-old. Build a review clause into your parenting plan to adjust the schedule as children grow.
Related Calculators
If you're going through a separation or divorce, you may also need to split assets and ongoing expenses. Use our divorce asset split calculator to divide property, retirement accounts, and debts between spouses. For splitting recurring child-related costs like education, healthcare, and activities between co-parents, try the co-parenting expense calculator.