Call Center Calculator

The Call Center Calculator – finds the number of agents needed to handle calls in a contact center while maintaining a preset service level or average speed of answer – a key part of Workforce Management (WFM). The key advantage of the calculator is accounting for abandonment rate. This feature works when traditional Erlang-C calculators will not help

The calculator takes into consideration three service objectives that could be satisfied simultaneously or in any combination when calculating staffing levels:

  • Service Level;
  • Abandonment Rate;
  • Average Speed of Answer.

Let us consider two examples demonstrating the advantage of accounting for abandonment rate:

A system that has the following parameters:

  • An arrival call rate is equal 2 call per second or 7200 calls per hour;
  • An average handling time is 3 minutes or 180 seconds;
  • A number of FTEs (agents) is 180.

According to Erlang-C this system is unstable and no service objectives could be evaluated. However, taking into consideration call abandonment makes this system stable. Applying the calculator we obtain:

  • Service level = 77.4%
  • Abandonment rate = 0.55%
  • Average speed of answer = 0.84 sec
  • Agent occupancy = 98%

So the system will work and only 0.55% of all calls will be abandoned.

Suppose the following input parameters:

  • An arrival call rate is equal 1 call per second or 3600 per hour;
  • An average handling time is 3 minutes or 180 seconds;
  • An average patience time is 180 seconds;
  • A number of full-time equivalents (FTEs/agents) is 181.

Then we have:

  • Service level = 63.3%
  • Abandonment rate = 1.37%
  • Average speed of answer = 2.13 sec
  • Agent occupancy = 98%

If we exclude abandonment (set average patience time to infinity) we will obtain average speed of answer equal to 7.69 sec. That increases waiting time threefold! Correspondingly the service level dramatically declined to 46.7%.

Here, taking into consideration call abandonment allows us to avoid overstaffing.


We are happy to answer questions, discuss specific workflows and requirements on a live presentation online, describe core benefits, or set up a pilot project to trial our applications without paying any license fees. Let Bright Pattern’s call center solution help you change the pattern of customer service