How to use this calculator
- Enter or choose hours open per day.
- Enter or choose days open per week.
- Enter or choose staff needed on duty at all times.
- Enter or choose staff on the roster.
- Enter or choose shifts per person per week.
- The coverage updates as you type. Use Copy result or Share to keep it.
Method
Needed = Hours open × Days open × Minimum staff; Delivered = Staff × Shifts × Shift hours × (1 − Shrinkage); Coverage = Delivered ÷ Needed × 100; Staff needed = ⌈Needed ÷ (Shifts × Shift hours × (1 − Shrinkage))⌉
- Shrinkage
- share of rostered time lost to leave, sickness, training and breaks
Worked example
- Needed = 12 × 7 × 3 = 252 staff-hours a week.
- Each person delivers 5 × 8 × 0.85 = 34 hours, so 8 people deliver 272 (107.94%).
- Staff needed = 252 ÷ 34 = 7.4, rounded up to 8.
Eight staff on five 8-hour shifts cover 108% of the 252 staff-hours needed, so the roster works with a 20-hour buffer.
What the result means
Coverage above 100% in total does not guarantee every hour is covered; check the rota so shifts line up with opening hours and peaks.
Assumptions and limits
- Demand is flat: the same minimum staffing for every open hour.
- Shrinkage is spread evenly across the roster.
- Peaks, skills mix, breaks within shifts and legal rest rules need a detailed rota or workforce-management tool.
Questions
What is shrinkage?
The share of paid, rostered time when people are not available to work: leave, sickness, training and meetings. Use your own history.
Why round staff up?
Because 7.4 people cannot be hired; 7 would leave hours uncovered. The fraction can also be covered with part-time staff or overtime.