Use this formula:
Parent A % = (Parent A overnights ÷ total overnights) × 100
Parent B % is the remainder (or compute the same way with Parent B overnights).
Example 1 — Exact 50/50
Over 14 nights, Parent A has 7 and Parent B has 7 → each is 50%.
Example 2 — Every other weekend
In a common 14-day primary-custody pattern, Parent B may have 3 overnights and Parent A 11 → Parent A ≈ 78.6%, Parent B ≈ 21.4%.
Example 3 — Annualizing a short sample
If Parent A has 7 overnights in 14 days, annualized overnights ≈ (7/14)×365 = 182.5. Use a full year when holidays and summers distort a two-week snapshot.
Run the free parenting time % calculator or generate a template on the schedule tools page to avoid spreadsheet errors.