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Using Excel to Calc Forecasted SLA


  • This topic has 3 replies, 2 voices, and was last updated 3 years ago by Saurabh.
Viewing 4 posts - 1 through 4 (of 4 total)
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  • #17155

    New to the board.

    I have recently taken over scheduling for an inbound call center with >4k employees world wide.

    My challenges include migrating two seperate scheduling functions and teams onto one scheduling platform, along with merging schedules of two previously seperate call centers

    With that, I have inherited several “tools” used by prior managers of the group that I have found to be providing incorrect informaiton to the business. One are our IDP’s (intra day performance reports) The majority of the IDP is constructed in TCS 6.3 but is then exported to Excel where they continue to tweak the numbers. One such tweak is an attempt to forecast SLA per interval (30 min). The math just doesn’t add up. I’ve tried some of the Excel Erlang calcs out there, but they seem to error out given the number of calls and advisors we have.

    Do any of you have any suggestions for a tool for excel that will allow me to calculate service level by interval if I know AHT, scheduled Staff, Call volume?

    Example of my interval volumes:
    Calls 1076, AHT 215, Staff 149,

    Thanks so much. I’m looking forward to learning a lot from this site.


    Hi Jamie,

    I would say that your SLA on that specific interval should be >99.00%.

    Unfortunately i don’t have any excel addons for this one.

    Tom Howard

    Hi Jamie, Magnus is right that the SLA is extremely high with your example – pretty much perfect performance. That’s no surprise because you have 149 staff ready to answer only 1076 (fairly short) calls in an hour. To answer your more general question, our company offers an Excel add-in for call center analysis called CC-Excel. This adds several functions to Excel that you can use to estimate call center performance.

    I’ve highlighted CC-Excel‘s SLA formulae below, in red:


    Function name Description
    CCXLAgents() Estimates the number of agents you need to handle incoming calls within specified service level parameters.
    CCXLCalls() Estimates the number of calls that your inbound call center can handle within specified service level targets.
    CCXLDuration() Estimates the average length call that your call center can handle.
    CCXLASA() Estimates the average speed in which your center’s calls will be answered.
    CCXLQueue() Estimates the average number of your inbound calls that will be queued and waiting for presentation to an agent.
    CCXLOccupancy() Estimates the percentage of their time that your call center’s agents will be busy handling inbound calls.
    CCXLAllBusy() Estimates the percentage of calls that will arrive while all your agents are occupied, and will therefore enter a queue.
    CCXLService() Estimates the percentage of calls that will be answered within a specified service time.
    CCXLLines() Estimates the number of telephone lines that are required to handle the inbound calls into your call center.

    CC-Excel’s strength is the flexibility and freedom it gives you to design workbooks that meet your exact requirements, rather than being tied to the formats and assumptions of Windows workforce management applications. With some knowledge of Excel, you can use its more advanced features such as lookup tables, conditional formatting and charting to build complex modelling tools.


    All the best,
    Tom Howard,
    Westbay Engineers Ltd.



    I have a query on the same lines as Jamie…

    I wish to optimise the overtime in my organisation. Hence I am working on a tool which can help provide data that if the overtime was not accrued for a particular interval… what impact it will have on actual Service Level. Example as below….

    The below data is past dated and have taken Actuals data.

    Actual SL = 93%,
    Call Volume = 4653,
    AHT = 230,
    Total Scheduled FTE = 615,
    Shift Scheduled FTE = 575,
    Overtime FTE = 40,
    Service Time = 30,
    Interval = 30 mins

    So…. We are looking at a scenario where if we hadn’t accrued the 40 agents from Overtime FTE, what impact it will create on ServiceLevel which ended at 93%. How much lower the Service Level will drop if Overtime was not accrued on that particular interval. I tried the SLA formula using Erlang but it didn’t work….

    Is there any other calculation wherein I can figure out the impact on SL if OT was not accrued.

    Thank You


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