About the Custody Percentage Calculator
This custody percentage calculator converts a parenting plan into the number of overnights each parent has in a year and the resulting time-share percentage. Choose a common schedule — every other weekend, 5-2, 4-3, or a 50/50 rotation such as 2-2-3 or alternating weeks — or enter a custom number of nights per two-week cycle, then add any extra holiday or summer overnights.
Overnight counts matter because many child support formulas switch on parenting-time thresholds. Canada’s Federal Child Support Guidelines use 40% (146 overnights), the UK Child Maintenance Service reduces payments from 52 nights a year, and many US states apply a shared-parenting adjustment once the paying parent passes a set number of overnights. Knowing the exact figure helps when drafting or negotiating a parenting plan.
The calculator assumes the regular schedule runs all year (365 nights ÷ 14 × nights per cycle) and adds net extra nights on top. Courts usually count overnights, but some jurisdictions count hours or days, so confirm the method your court uses.
With the default inputs, the parent b parenting time is 32.4%. Change any value above to recalculate instantly.
How to use the custody percentage calculator
- 1Pick the regular schedule, or choose custom and enter Parent B’s overnights per two weeks.
- 2Add the net extra overnights Parent B gets for holidays, school breaks and summer.
- 3Read each parent’s overnights and percentage of parenting time.
- 4Check the thresholds table to see which support adjustments the schedule meets.
Formula and method
A repeating parenting schedule is reduced to the number of overnights Parent B has in a two-week cycle. Multiplying by 365 ÷ 14 (about 26.07 cycles) gives the yearly overnights from the regular schedule. Holiday, vacation and summer time that departs from the regular schedule is added as net extra nights. Parent A has the remaining nights of the 365-night year.
The percentage is Parent B’s overnights divided by 365. Results are shown to one decimal place rather than rounded to whole nights, so a 50/50 rotation shows exactly 182.5 nights. Leap years and schedules that do not repeat every two weeks will differ slightly.
- Nights per 14 days
- Parent B overnights in one two-week cycle of the regular schedule
- Extra nights
- Net additional overnights from holidays and summer
Worked examples
Every other weekend plus a midweek overnight, 14 holiday nights
Four overnights every two weeks is 4 × 365 ÷ 14 = 104.29 nights. Adding 14 holiday nights gives 118.29 overnights, or 32.4% of the year.
Every other weekend only
Two overnights every other weekend is 52.14 nights a year, about 14.3% — just over the UK’s 52-night shared-care threshold.
2-2-3 rotation
A 2-2-3 rotation gives each parent 7 of every 14 nights, so each has 182.5 overnights and 50% of parenting time.
Frequently asked questions
How many overnights is 40 percent custody?+
40% of a 365-night year is 146 overnights. That is the threshold for shared parenting under Canada’s Federal Child Support Guidelines and close to the shared-custody thresholds used in several US states.
What percentage is every other weekend?+
Every other weekend from Friday to Sunday is two overnights every two weeks, about 52 nights a year or 14.3%. Adding one midweek overnight every week doubles it to around 104 nights, or 28.6%.
Do holidays and summer count toward custody percentage?+
Yes. Courts and support agencies count every overnight during the year, so summer blocks and holidays that differ from the regular schedule should be included. Enter them as extra nights.
Why does custody percentage matter for child support?+
Many child support formulas reduce or recalculate support once the paying parent has enough parenting time. For example, the UK CMS reduces payments from 52 nights a year, and Canada uses a set-off approach at 40% parenting time.
Results are general estimates and not legal advice. Laws vary by jurisdiction — consult a qualified attorney.