There are many ways to calculate a contact centre time to answer SLA. One of the key differences between common approaches is how we treat abandoned calls.

Here we will cover off all common methods and discuss pros and cons.

One thing we must point out is that we want to include the IVR time as part of the wait time. As far as the customer is concerned they are waiting after they dialled the number. Ignoring the IVR time does not give us the full picture of customer’s experience throughout the call and does not encourage our organisation to look at the entire call i.e. optimise our IVR as well as improve our answer times.


SLA Calculator 1 – Ignoring abandoned calls

This method simply works out the ratio of calls answered within the pre-defined SLA period to the total number of calls offered. SLA calculations can be performed by organisations with limited or outdated platforms which cannot track abandoned calls, this however exculdes a significant portion of customers and does not make for an accurate measure.

SLA = Calls Answered Within Predefined Time / Total Calls


SLA Calculator 2 – Offered calls exclude calls abandoned within the SLA period

In our opinion, this method does not give a true Service Level representation. If the call was abandoned before it was answered, whether the abandon was caused by the system, or the IVR was too difficult to understand so the customer terminated the call the mselves, the end result is that the customer never got through. This method is sometimes used when an SLA is considered to be a contact centre performance indicator rather than measure of the service being offered to customers. In this case counting abandoned calls is seen as penalising the contact centre for what is outside of their control rather than highlighting improvement opportunities to teams who manage the IVR.

SLA = Calls Answered Within Predefined Time / (Total Offered Calls – Abandoned Calls)


SLA Calculator 3 – Offered calls include all abandoned calls

From a customer’s point of view this method best reflects the time to answer service level. Changes anywhere in the customer’s journey will impact the SLA whether it’s the IVR or the time it takes by the contact centre to answer the call.

SLA = Calls Answered Within Predefined Time / (Total Offered Calls + Abandoned Calls)