Child Custody Time-Share Calculator

Time-share percentage is the share of overnights each parent has with the children annually. It's the standard input that family courts and child-support calculators use to adjust support amounts — and the higher your time-share, the lower your support obligation in most states.

How Time-Share Is Counted

Most states count overnight stays (where the child sleeps), not waking hours. A parent with the child from 8am Saturday until 7pm Sunday has one overnight, not two. School-year overnights are computed from the parenting plan (e.g., every other weekend = 2 overnights per 14-day cycle = 52 nights/year over 36 school weeks).

Time-Share Thresholds by State

California: full support adjustment above 30% time-share via Dissomaster. Texas: ~50% threshold for split custody adjustment. Illinois: 40% threshold for shared parenting modification. Florida: 73 overnights (20%) triggers credit. Each state has its own formula; this calculator gives you the input — your local guidelines do the math.

The Most Common Counting Error: Double-Counting Holidays

The mistake that inflates almost every self-calculated time-share is counting the same night twice. Major holidays sit inside the school year, so if your regular rotation already gave you a Thursday-to-Sunday and you then add Thanksgiving as extra holiday nights, those nights are in the total twice. Count a holiday night only when it replaces what your ordinary schedule would have given you — a Christmas week you would not otherwise have had, or a spring break that overrides the normal rotation. The calculator above now flags it when your entries add to more than 365 nights, which is the clearest symptom of this error.

Two related conventions matter just as much when a court or a support formula reads your figure. First, an overnight is credited to whoever has the child where the child sleeps, so a parent who collects a child after school, provides dinner and returns them at 8pm has had a valuable day of parenting time but zero overnights — many parents are surprised how much daytime contact produces no time-share credit at all. Second, the count that matters is the schedule actually exercised, not the one written in the order; courts routinely adjust when the practice has diverged from the paper. If your real pattern differs from your parenting plan, calculate both figures before relying on either one. Last reviewed 21 August 2026.

Document Your Time

Use a co-parenting app (OurFamilyWizard, TalkingParents, Custody X Change) to log actual overnights. Courts give weight to consistently exercised time-share. If your parenting plan grants you 40% but you only actually take 25%, expect support to be calculated on the actual exercised time.

Overnights Per Year for Common Parenting Schedules

Before you negotiate, know what each standard schedule actually produces over a full year. Every other weekend (Fri–Sun) gives the non-residential parent 2 overnights per 14 days, about 52 nights or 14.3%. Every other weekend plus one midweek overnight reaches roughly 78 nights or 21.4% — which is what pushes a Florida parent past the 73-overnight credit threshold. Extended alternate weekends (Thu–Mon) reach about 104 nights or 28.6%, just under California's 30% adjustment point. 5-2-2-5, 2-2-3, and week on / week off all produce 182 or 183 nights, an even 50%. Summer and holiday blocks are added on top of the school-year cycle, and they are usually what moves a schedule across a threshold — four extra summer weeks alone is 28 overnights, or 7.7 percentage points. Enter each block separately in the calculator above rather than estimating a single annual percentage, because the thresholds below are decided by the exact overnight count, not by a rounded figure.

Why the Exact Overnight Count Matters More Than the Percentage

Several states apply their support adjustment at a hard cutoff rather than on a sliding scale, so a single overnight either side of the line can change the annual support figure by a meaningful amount. Florida's statute grants substantial time-sharing treatment at 73 overnights — at 72 the standard formula applies, at 73 the alternate one does. That is why courts and support software count nights rather than accept a percentage: 20% of 365 is 73.0, and rounding a schedule described as “about 20%” can land on the wrong side. Two further points routinely catch parents out. First, courts generally calculate on the time actually exercised, not the time granted — a plan awarding 40% that you exercise at 25% will usually be recalculated at 25%. Second, leap years contain 366 days, so a 50/50 schedule gives one parent 183 nights and the other 183, but an odd-numbered schedule shifts by a night. Verify your state's threshold and its rounding rule with the state guideline itself before relying on any calculator, this one included.

Last updated 2026-08-12. Sources: California Courts self-help — child support, Texas Family Code Ch. 154, Florida Statutes § 61.30 (73-overnight substantial time-sharing threshold).