WFM guideCapacity planning

Contact centre net staffing

Q: What is the difference between net staffing and gross staffing in a contact centre?

In contact centre workforce management, net staffing (or the net requirement) is the number of agents that must be actively on-phone at a given moment to meet the service level target — the output of an Erlang C calculation or equivalent model. Gross staffing (or total headcount requirement) is the number of employed agents the operation needs in order to consistently deliver the net requirement, after accounting for all the factors that reduce the proportion of time each agent spends on-phone: shrinkage (absence, leave, training, meetings), part-time working (agents contracted for fewer hours than a full-time equivalent), ramp time for new starters (agents who are employed but not yet fully productive), and attrition uplift (additional headcount in the recruitment pipeline to replace agents who will leave during the planning period). The ratio of gross to net headcount — called the gross-up factor or staffing multiplier — is typically 1.25 to 1.45 in a well-managed contact centre, meaning you need 25–45% more employed agents than you need on-phone at any given moment.

The Erlang C answer tells you how many agents need to be on-phone to meet your SL target. It does not tell you how many agents to hire. The gap between those two numbers — filled by shrinkage, part-time ratios, attrition, and ramp time — is what the gross-to-net calculation exists to close.

The gross-to-net staffing calculation

Worked example: Monday peak, voice channel

Step 1: On-phone requirement (Erlang C output)

50 agents

The number of agents that must be actively handling or available for contacts during the peak 30-minute interval to deliver the SL target (e.g. 80% answered in 20 seconds).

Step 2: Gross up for shrinkage

50 ÷ (1 − 0.27) = 68.5 → 69 agents rostered

If total shrinkage is 27%, only 73% of rostered agents are available for contacts at any moment. Divide the on-phone requirement by (1 − shrinkage rate) to find the number that must be rostered.

Step 3: Convert to FTE if the workforce includes part-time

69 rostered positions ÷ 0.85 FTE average = 81.2 → 82 FTE required

If part-time agents average 0.85 FTE contracted hours per full-time equivalent, more headcount is needed to deliver 69 rostered positions. Divide by the average FTE fraction of the workforce.

Step 4: Add ramp-time uplift for new starters

82 × 1.08 = 88.6 → 89 FTE required

New agents are typically at 50–70% productivity for their first 4–8 weeks. If 10% of the workforce is in ramp at any time and performing at 60% productivity, the effective ramp penalty is approximately 4% on total headcount — add an uplift factor.

Step 5: Add attrition uplift for the planning period

89 × 1.05 = 93.4 → 94 FTE — the recruitment target

If annual attrition is 25% and the planning period is 3 months, expected leavers = 89 × 0.25 × 0.25 = 5.6 → 6 agents. 94 is the total headcount target entering the planning period to exit with 89 fully productive agents.

Result: An on-phone requirement of 50 agents translates to a recruitment target of 94 FTE — a gross-up multiplier of 1.88. This is on the high side (typical range 1.25–1.45) because the worked example uses relatively high shrinkage (27%) plus part-time adjustment plus ramp plus attrition. Real operations should calibrate each input to their own data.

Common errors in net staffing calculations

Using total headcount as the on-phone requirement

The recruitment target equals the on-phone requirement — shrinkage, part-time, and ramp are not applied. The operation is structurally understaffed from day one. This is the most common net staffing error and the most damaging.

Using a single shrinkage figure for the whole year

Shrinkage varies seasonally — absence rates are typically higher in Q1 (winter illness) and Q3 (summer leave peak). A single annual average shrinkage figure will produce a slightly understaffed Q1/Q3 and slightly overstaffed Q2/Q4.

Not accounting for ramp time in new starter cohorts

A new starter performing at 60% productivity for 8 weeks costs the operation 0.4 FTE for 8 weeks. If 20 agents are hired in a single cohort, the ramp-time capacity gap is 8 FTE for 8 weeks — equivalent to approximately £40k in agency or overtime cost at typical UK contact centre rates.

Double-counting attrition in the planning model

Some operations include attrition in both the shrinkage figure (as absence before leavers are formally processed) and as a separate attrition uplift. The result is an overstated recruitment target — leading to overstaffing and the associated cost.

Net staffing questions

What is the difference between net staffing and gross staffing in a contact centre?

Net staffing (the net requirement) is the number of agents that must be actively on-phone at a given moment to meet the SL target — the Erlang C output. Gross staffing (total headcount requirement) is the number of employed agents needed to consistently deliver the net requirement, after accounting for shrinkage, part-time ratios, ramp time, and attrition. The ratio of gross to net — the gross-up factor — is typically 1.25 to 1.45 in a well-managed contact centre. You need 25–45% more employed agents than you need on-phone at any given moment.