Capacity inputs
One month at a time, per line of business.
Headcount to fund, including shrinkage and target occupancy.
On-phone requirement before shrinkage is added back.
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Results are estimates for planning purposes only and should not replace professional workforce management judgment.
Capacity planning answers a budget question rather than a rostering one: how many people do we need to fund next month, next quarter or next year to serve the forecast volume? Unlike Erlang C, which models a single interval, capacity planning works in aggregate hours over a whole month.
Step by step
- Workload hours = (monthly volume × AHT) ÷ 3600. This is the raw handling time the month demands.
- Gross hours per FTE = working days × shift length. What one full-time person is paid for.
- Net productive hours per FTE = gross hours × (1 − shrinkage) × target occupancy. What one person actually delivers in handling time.
- Required FTE = workload hours ÷ net productive hours per FTE.
Why occupancy belongs in the denominator
Nobody handles contacts back-to-back for an entire available shift. Dividing by a target occupancy of 85% acknowledges the idle time that queueing behaviour makes unavoidable , the same idle time Erlang C predicts at interval level. Omit it and your plan will look roughly 15% cheaper than reality, which is the single most common cause of an under-funded contact centre.
What this number is and is not
The FTE figure is a funding and hiring number. It does not guarantee your service level, because it says nothing about when those people work. Two operations with identical FTE can produce very different service levels depending on how well their rosters match the intraday arrival pattern. Use capacity planning to decide how many people to hire, then use Erlang C by interval to decide where to place them.
Practical adjustments
- Add an attrition allowance: divide by (1 − expected monthly attrition) if you need average headcount to hold through the month.
- Plan the training pipeline backwards from your ramp-up time, new hires are not productive on day one.
- Run the model per skill or line of business, then sum. Blending very different AHTs into one average hides the real requirement.
- Re-run monthly against actuals; forecast accuracy, not the formula, is what usually breaks a capacity plan.
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