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Optimal staffing model

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    Jessica Branco

    I am looking at setting up an optimal staffing model. Any ideas or examples would be appreciated.

    Joe Barkai


    The most common staffing model is based called Erlang C and is based on the “loss formula” developed by Erlang. There are many extensions to the original formula and to the Erlang C model to allow forecasting multiple call center key performance indicators. As the calculations are somewhat complex and can be tedious, this is best done by software. You can read about the actual model in

    The modeling process starts with a target service level, e.g. 80% answered in 30 seconds. Because this metric does not reflect abandonment rate, some choose to include maximum abandonment rate as a target as well. Another input is the expected call volume and handling time.

    The Erlang C model calculates the number of agents that are required to meet or exceed the target service level. The modeling software should also calculate ASA and utilization (occupancy rate). If the calculated headcount, abandonment or utilization is too high, you change the targets and recalculate until you find an acceptable balance between service levels, resource availability, and utilization.

    Some Erlang software tools calculate additional parameters such as time in queue and provide additional insight of the customer experience for a given service level target and headcount.

    I hope this helps.


    Vijay Swami

    Hi Jessica,
    Not sure if you are still looking at an answer to this problem. First you need to have all the inputs right . The following are the inputs you would need

    1. Average daily Forecasted Call Volume
    2. Average Handle time for the calls (Talk Time+After Call Work time)
    3. How many hours is your center open?
    4. What kind of Schedule adherence you plan to achieve?
    5. What kind of Shrinkage (time for breaks etc) you want to use?
    6. What kind of Service level you want to achive?

    Once you have all these major assumptions you can use an Erlang-C model and calculate the Staffing and see if the Occupancy level is acceptable to you
    Feel free to ask me any further questions

    Eloi Hizon


    I’m looking at getting a formula in removing Service Level % as a factor to derive at a number of heads required.

    Basically, if I have x number of calls to be answered in 60 seconds or less, with an AHT of 8 minutes, what’s my headcount?

    All formula that I have is asking for Service Level % which, in this case, is not a target, only ASA.

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