Shift Staffing Calculator

How shift staffing and the relief factor work

Coverage is the number of people who have to be working at any given moment. Staffing is the number of people you have to employ to deliver that coverage. The two are different because no one works every hour of the year. Once you take out weekends and days off, vacation, holidays, sick time, and training, each person only fills part of the hours a post needs, so it takes more than one employee to keep one seat filled around the clock.

Coverage hours divided by what one person works

The method here is the standard relief factor approach. First it works out the coverage hours a post needs in a year, the hours per day times the days per week times 52. A single position open 24 hours a day, 7 days a week needs 8,736 hours of coverage a year. Then it works out the hours one employee works after time off. Dividing the first by the second gives the relief factor, the number of employees it takes to keep one position filled. Multiply by the positions you must cover and round up, and you have the headcount.

Why the number is bigger than the schedule

A schedule shows the slots: two positions on three eight-hour shifts looks like six people. But those six slots run every day of the year, and the people filling them take days off and leave. That is why an around-the-clock post that looks like six slots usually needs ten or eleven employees. The gap between the slots you see and the people you need is exactly what the relief factor captures, and ignoring it is what forces the overtime.

Set the assumptions from your own data

A relief factor near 1.4 to 1.6 per eight-hour shift is common for moderate leave use. Much above 1.7 usually means heavy time off, lots of training, or a schedule that could be tightened. Track your real leave usage and absence rate, then set the time-off days to match, because that is what moves the number most.

How many people does it take to cover one position 24/7?

A common rule of thumb is about 5 employees per around-the-clock position once days off and time off are counted, sometimes stated as 5.4. The exact number depends on how much leave your people take and your shift pattern, which is what this tool calculates from your own inputs.

What is a relief factor?

It is the number of employees needed to keep one position filled, after accounting for the hours each person is off. A relief factor of 1.0 means no backfill is needed, as with a single weekday desk. Continuous coverage pushes it well above 1.0.

Why not just schedule the shifts I can see?

Because the slots on a schedule run every day, and your people do not. Staffing only to the visible slots leaves no one to cover days off, vacation, or sick days, so the gap gets filled with overtime, which usually costs more than the extra hire.

Does this account for demand peaks?

No. This sizes coverage you set as a fixed number of positions. For demand that swings through the day, like call volume, a queue model such as Erlang is the right tool to set how many positions you need first, then this tells you how many people to staff them.

Is this HR or scheduling advice?

No. It is a planning estimate built on the standard relief factor method. Calibrate it to your operation and confirm overtime and scheduling against the wage and hour rules that apply to you.