Forecasting contact centre demand is rarely as simple as plugging numbers into a calculator.
In this instalment of our video series on the key concepts behind accurate forecasting, Call Centre Helper’s Jonty Pearce explains average handling time (AHT) and how calls are really distributed.
This topic is often misunderstood, yet it’s crucial for accurate workforce planning.
Video: Forecasting Fundamentals: AHT and Call Distribution
Watch the video below to hear Jonty explain what you need to know about forecasting – focussing on AHT and call distribution:
The AHT Misconception
Many people assume that AHT follows a normal distribution. If the average handling time is five minutes, they expect most calls to last about five minutes, with a smaller number of shorter and longer calls either side, as Jonty explains:
“Here’s a misconception that a lot of people have about average handling time: so, you’ve got an average handling time of five minutes, and a lot of people think that the average handling time of five minutes is distributed sort of like this, something like a normal distribution.
You’ve got a lot of calls around here, and then it sort of tails off accordingly. Unfortunately, that is not at all how average handling time is distributed. It’s not even distributed like this. You might have heard it’s a Poisson distribution, so it’s not a lopsided distribution.”
Some think it follows a lopsided shape, such as a Poisson distribution. Both assumptions are incorrect.
The Erlang Distribution
In reality, AHT follows an Erlang distribution, which means that calls are not grouped closely around the average, as Jonty continues:
“What you actually have with average handling time is you have what is called, funnily enough, the Erlang distribution.
So, you have your average handling time of five minutes, but actually there aren’t many calls distributed around the average.
What you find is a lot of short calls, people who’ve got very simple enquiries and they call in and get those answered very quickly, and what you also have is some very long complex enquires.”
Instead, contact centres see a large number of short calls, often for quick, simple queries. These are balanced out by a smaller number of much longer calls that deal with more complex issues.
This creates a skewed distribution, where the average is not a reliable indicator of the most common call lengths.
The Impact on Forecasting
This uneven distribution affects how many agents are actually needed.
“What that tends to have an effect on is that you get very skewed results, so for instance although an Erlang calculator will say you need 208 agents, what you’ll actually find is that the average number of agents that you need will vary quite considerably from what the Erlang calculator will say.
The Erlang calculator will tend to give you an average number of people you need, but that could vary by sort of plus or minus 10% quite dramatically.
Depending on how many short calls you get in that period, or how many long calls you get in that period, across a long enough time period, it will tend to average out like this and that is called the Erlang distribution.”
While an Erlang calculator might tell you that 208 agents are required, that figure is an average. In practice, the number of agents needed can vary by as much as plus or minus 10%.
That variation depends on the call mix during any given period – how many short, quick calls versus longer, complex ones.
Over longer periods, the numbers tend to balance out. But in shorter timeframes, relying only on average figures can lead to inaccurate staffing and poor service levels.
Why It Matters
Understanding the true distribution of AHT helps contact centres forecast more effectively.
It highlights the need to go beyond averages and plan for fluctuations in call type and length. This approach leads to better resource management and improved customer service.
If you are looking for more great insights from Jonty about forecasting, check out these next:
- Getting Started With Forecasting
- Is Overhang Distorting Your Staffing Calculations?
- Why Your Forecasters Should Always Talk to Marketing
Author: Jonty Pearce
Reviewed by: Robyn Coppell
Published On: 17th Sep 2024 - Last modified: 19th May 2025
Read more about - Video, Average Handling Time (AHT), Forecasting, Top Story, Videos
