The staffing formula – and what it leaves out
The staffing formula reads: gross staffing demand in full-time equivalents = (hours to be covered per year ÷ net annual working time of one full-time employee) × absence factor. “Net” refers to the annual working time here, not to the staffing demand. What matters is not the formula itself but how honestly its two inputs are determined — and that absence is counted exactly once, either in the net annual working time or in the absence factor. In regulated sectors, separate statutory methods apply alongside it; these notes do not replace legal or collective-bargaining advice.
The formula at a glance
Hours to cover ÷ net annual hours × absence factor
Gross minus leave, public holidays, training
1 ÷ (1 − absence rate)
Gross demand in FTE
Where the calculation breaks down in practice
The calculation uses gross annual working time – leave and public holidays are missing
Net annual working time: gross minus leave, public holidays and training
The absence allowance is guessed instead of derived from your own numbers
An absence factor as the inverse of availability, calculated with your own absence rate
The result describes an average day, not the peak
Staffing levels per shift type and weekday instead of a single average
The result sits in a spreadsheet and never reaches the schedule
The target staffing level becomes a planning rule that every schedule is checked against
Spreadsheet calculation vs. rule in the schedule
| With vigotime | Spreadsheet calculation | |
|---|---|---|
| Target staffing | Configured per shift type and weekday | One average for every day |
| Effect | The target staffing checks every schedule | The result stays in the spreadsheet |
| Understaffing | Shows up while planning | Shows up during the month |
| Maintenance | One configured rule for all schedules | Every copy of the file lives on |
Can you beat the schedule?
Staff a mini week with early, late and night shifts — then see what automated planning changes.
Early
Late
Night
Mon
E + L + N
Tue
E + L + N
Wed
E + L + N
Thu
E + L + N
Fri
E + L + N
Frequently asked questions about staffing calculation
Gross staffing demand in full-time equivalents = (hours to be covered per year ÷ net annual working time of one full-time employee) × absence factor. The hours to be covered follow from target staffing per shift times shift length times number of days. “Net” describes the annual working time, not the staffing demand.
Gross annual working time minus leave, public holidays and training. For a 39-hour week the gross figure comes to roughly 2,030 hours (39 × 52); after the deductions above, noticeably less remains. Sick days belong either here or in the absence factor — never in both. The actual values depend on region, collective agreement and works agreement; these notes do not replace legal or collective-bargaining advice.
From your own absence rate rather than from a rule of thumb. The factor is the inverse of availability: 1 ÷ (1 − absence rate). At 6 per cent that is 1 ÷ 0.94 ≈ 1.064. The shortcut “1 + rate” is close for small rates but clearly underestimates demand as soon as the rate reaches double digits.
Assume a unit staffed around the clock: three 8-hour shifts with 2 people each, so 48 hours to cover per day and 17,520 per year. A full-time employee on a 39-hour week has 2,028 gross hours; after deducting 30 days of leave, 11 public holidays and 5 training days at 7.8 hours each, roughly 1,669 hours remain. At a 6 per cent absence rate the factor is 1.064. The calculation: 17,520 ÷ 1,669 × 1.064 ≈ 11.2 — around 11 full-time equivalents of gross staffing demand. All input values are placeholders to be replaced with your own.
Usually because it works with averages. Demand, however, arises per shift type and weekday: a night shift at the weekend needs different staffing than a Tuesday morning. An annual calculation across everything hides exactly those peaks.
As a business calculation, yes — but separate regulated methods apply there as well: staffing assessment under section 113c SGB XI in residential care, and PPR 2.0 plus minimum nurse-staffing levels in hospitals. Those methods set requirements; the formula above tells you how many full-time equivalents your schedule actually needs. Which requirement is binding for your organisation is a legal question.