Shift Roster Staffing Calculator
How many people it takes to keep a position filled across a roster — from the hours to cover each week, the positions on each shift, contracted hours per person and an allowance for leave and absence — with the headcount, the real hours each person works and the cost.
A 24/7 position is 168 hours a week.
How the shift roster staffing calculator works
A 24/7 position is 168 hours a week. One person on contracted hours covers about 38 of them, and leave, sickness and training take a share of those, so the full-time equivalents needed are the coverage hours over the hours a person actually delivers. Round up for whole people, and the rounding is where rosters gain their slack — or lose it.
Formula: FTE = coverage hours × positions / (contracted hours × (1 − allowance)); headcount = ⌈FTE⌉
Worked examples
| Inputs | Headcount required | Note |
|---|---|---|
| Two people, around the clock | 11 | eleven people |
| Business hours only | 2 | two people |
| Twelve-hour shifts | 11 | fewer, longer shifts |
FAQFrequently asked questions
How many people does a 24/7 position need?
About 5.5 full-time equivalents per position once leave and absence are allowed for — so two positions need eleven people, not ten.
What allowance should I use?
Annual leave, public holidays, sick leave and training together take 12 to 20% of contracted hours. Use your own absence figures; the default of 15% is a typical starting point.
Why round up?
Because half a person cannot work a shift. The surplus hours from rounding are the roster's slack — useful, but they are also paid.
Does shift length change the headcount?
Not the hours — the same position-hours need the same people. It changes how many shifts each person works and how the roster fits together.
What about overtime instead of headcount?
Overtime covers gaps but at premium rates and with fatigue. The cost-per-covered-hour row is the figure to compare an overtime plan against.
Where these figures come from
- CIPD — Employee turnover and retention factsheet — the turnover and stability index definitions used here
- Acas — the UK workplace advice service
Last checked: September 2026. These are standard management definitions; where practice varies, the page says which convention it uses.