Agents FTE In Call Centre Helper Excel Calc Jumps

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Agents FTE In Call Centre Helper Excel Calc Jumps From 6 to 8

I’m using the call-centre-helper-erlang-calculator-v5.5.xlsm and noticed that the FTE with shrinkage(=AgentsFTE) will jump by 2 agents. For example:

  • Calls:14
  • Reporting Period:60
  • AHT:577
  • Required Service Level:80%
  • Target Answer Time:60
  • Shrinkage:35%

= Agents FTE of 6

If I increase the AHT to: 578

then Agents FTE jumps to 8.

How should I interpret this?

Question asked by Lex

You Are Seeing the Effects of Shrinkage

What you are seeing here is the effect of 35% shrinkage and a particular threshold.

It’s easier to see this using the Online Erlang calculator

So 14 number of calls per 60 minutes = 2.244 Erlangs – AHT 577 secs – 80% Answered in 60 secs – Shrinkage 35% – Max Occupancy 85%.

Gives 4 Agents before Shrinkage = 6 agents after shrinkage

Increase the AHT by one second takes you over a threshold

14 number of calls per 60 minutes = 2.248 Erlangs – AHT 578 secs – 80% Answered in 60 secs – Shrinkage 35% – Max Occupancy 85%.

Gives 7 Agents before Shrinkage = 7.5 agents after shrinkage

In the case of The Excel calculator this rounds it up to 8.

Looking at the chart at the bottom of the Online Calculator if you had 4 agents before shrinkage (6 agents after shrinkage) you would have a service level of 79.9% which is just below the 80% threshold which is why it adds one agent before shrinkage.

So the issue is around how you round the number of agents with shrinkage.

4 Agents before 35% shrinkage = 4 / ( 1 – 0.35) = 6.15 Agents after shrinkage

5 Agents before 35% shrinkage = 5 / ( 1 – 0.35) = 7.69 Agents after shrinkage

One agent before shrinkage will add 1.54 agents after shrinkage. So depending on how you round up the number of agents will give different results.

So the calculator is working as intended, but that is one of the challenges with Erlang as it works in increments of 1 agent before shrinkage.

You should find that the Online Calculator will give better results.

With thanks to Jonty


Thank you very much for the explanation. I thought it was something like that but the confirmation was super helpful as my experience here is limited. Yes, the Excel function can only return one thing vs the On-Line Calculator can return the table

Very much appreciated.

With thanks to Lex

Author: Jonty Pearce

Published On: 12th Apr 2022 - Last modified: 18th Jul 2022
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