How to Calculate Contact Centre Service Level


In this article, we will provide you with the best formula, methods and advice on how to calculate service level (SLA) in the call centre.

In actuality, call centre service levels are quite easy to calculate in the contact centre, but there has been a lot of confusion on how to measure them.

The Service Level Formula

The service level formula is simply the number of calls answered within the service level threshold divided by the number of calls offered, multiplied by 100.

Service Level = (Number of Calls Answered Within the Service Level Threshold ÷ Number of Calls Offered) x 100

Service level formula: Service level = number of calls answered within the service level threshold divided by number of calls offered

This then gives you a percentage service level.

It’s really as easy as this.

For example, if a company has an objective to answer 80% of all calls within 20 seconds, the Service Level Threshold is 20 seconds.

Worked Example

Both of the pieces of information used in the calculation below can be taken from the contact centre’s Automated Call Distribution (ACD) system or, failing this, can be gathered from Call Detail Records (CDRs).

Number of calls answered within the service level threshold = 136
Number of calls offered = 170

Service level calculation: 136 divided by 170 times 100 is 80% service level

A worked example of the service level formula

A new service level should be calculated for each new reporting period, which for most contact centres would be every half hour, if it is impossible to do so in real time.

By doing this, the contact centre can see whether or not they have the correct number of advisors to handle varying call volumes throughout the day.

To calculate staff numbers to meet a target service level, read our article: How to Work Out How Many Staff You Need in a Contact Centre

Should Calls That Abandon Within Five Seconds Be Discounted?

Some algorithms ignore short abandoned durations of less than 5 seconds in their service level calculations.

Dave Appleby

Dave Appleby

This is because people may have dialled the wrong number in error and then hung up. This can be configured on many ACD systems.

This is generally seen as being OK.

“It’s less than one ring cycle and some ACDs may not have even delivered it to a turret even though the customer is hearing a ring,” said Dave Appleby, an experienced resource planner.

So, excluding short abandoned calls, the revised formula becomes:

Revised service level formula: Number of calls answered within the service level threshold divided by (the number if calls offered - number of calls abandoned in less than 5 seconds) times by 100

The Service level formula that takes short abandoned calls into account

Should ALL Abandoned Calls Be Excluded?

The short answer to this is no.

An abandoned call is a call that has been offered and you had the chance to answer it.

The rate at which calls abandon, though, does, unsurprisingly, vary according to call type. This is highlighted in the graph below.

A graph showing abandon rates vs service levels for different call types. The graph shows a downward curved line from the top right corner to the bottom left corner

As all of the lines seem to meet at 80%, it is no wonder this has become the industry standard.

Follow the link to find out: How to Predict Call Abandon Rates Based on Service Level

Timing Generally Starts After the IVR Selection

Generally, the service level time starts post-IVR selection.

Service level is based on ‘Of the calls you COULD have answered, how many were answered in x seconds?’

Dave Appleby

“I’ve not come across anyone who does it the other way. The rationale being that service level is based on ‘Of the calls you COULD have answered, how many were answered in x seconds?’,” said Dave Appleby.

However, keeping a separate track of the number of calls that “drop-out” of the IVR can be be a useful measure of its effectiveness.

Industry Standards for Service Levels

  • Phone: 80% of calls answered within 20 seconds
  • Email: 100% of emails answered within 24 hours
  • Live Chat: 80% of chats answered within 20 seconds
  • Letters – 95% of letters answered within three days
  • SMS/messaging apps – 80% of messages responded to within 20 seconds

Be Careful With ACD Stats

On certain ACD systems the service level displayed on the wallboards could be misleading.

For example – you have a service level target of 80% of calls answered in 20 seconds. A 100% service level figure on your ACD stats does not mean that 100% of calls were answered within 20 seconds.

The 100% figure actually means that 100% of calls met the service level target (i.e. 100% of 80% of calls were answered within the target). Similarly, a service level figure of 80% may only mean that 64% of calls (80% of 80%) were answered in the threshold time. This has certainly confused many people.

In this case, it would be safer just to display the percentage of calls answered within 20 seconds.

For more advice on this topic, read our article: What Information Should You Be Displaying on Your Contact Centre Wallboards?

Do You Have to Stick to the Industry Standards for Service Level?

As noted earlier, most contact centres stick to the industry standards of service level, which is to answer 80% of calls in 20 seconds.

However, there are signs to suggest that contact centres are starting to relax their service levels. According to our white paper, “What Contact Centres Are Doing Right Now“, the number of contact centre professionals who would consider service level as a “very important” metric has decreased from 70.0% to 62.7% in just twelve months.

Those who are thinking in this way could be questioning the impact of service level on Customer Satisfaction (CSat) and argue that spending more time on ensuring First Call Resolution (FCR) would please customers more than focusing on meeting a particular service level.

A C-SAT matrix showing the c-sat for whether the problem is resolved against the wait time (short, medium or long)

The table above was taken from our article: “Is There a Correlation Between Queue Time and Customer Satisfaction Levels?” And it demonstrates that queue times don’t have a major impact on customer satisfaction, as long as the call is resolved.

However, while this is a good case for not targeting advisors against time-based metrics, calculating service level is still an important part of workforce management (WFM) for many contact centres.

For more industry standards of common contact centre metrics, like service level, read our article: What Are the Industry Standards for Call Centre Metrics?

How People Manipulate Service Levels

As with all metrics, as soon as people see that a metric is important, then they will start to manipulate the results.

Here are the three most common ways that service level results are manipulated:

1. Excluding Abandoned Calls

The easiest way that people can fiddle the service level figures is to exclude abandoned calls from the calculation.

For example, the Cisco contact centre software allows for three different ways of calculating service level.

Abandoned Calls Have a Negative Impact on Service Level (This is the correct method)

The number of calls answered within the threshold divided by the number of calls that had a service level event. This treats these abandoned calls as though they had exceeded the threshold.

Abandoned Calls Have No Impact on Service Level (Should not be used)

The number of calls answered within the threshold divided by the number of calls that had a service level event minus the number of calls that were abandoned before exceeding the service level threshold. Calls abandoned before the service level threshold expired are removed from this calculation.

Abandoned Calls Have a Positive Impact on Service Level (Is used to manipulate service levels)

The number of calls answered within the threshold plus the number of calls abandoned within the threshold, all divided by the number of calls that had a service level event. This treats these abandoned calls as though they were answered within the threshold.

The right way to include abandoned calls. A green tick is above 'abandoned calls have a negative impact on service level', a red cross over 'abandoned calls have no impact on service level', and anther red cross above 'Abandoned calls have a positive impact on service level'

2. Changing the Targets (albeit temporarily)

I know of an on-the-spot decision by a director, who changed the service level from 90/15 to 80/20 and then recalculated the quarter just so they didn’t miss the target!

3. Putting in a Call-Screening Group

Some companies put in place a call-screening or triage group. This is similar to the company switchboard in that this quickly answers the calls before transferring them to a longer queue in the appropriate department.

This is sometimes used to cover up service level problems. For example, a few years ago, one of the regulators put in place a metric on the speed of answer of telephone calls.

Originally published in January 2017. Recently updated. 

For more insights into contact centre service levels, read our articles:

Author: Jonty Pearce
Reviewed by: Megan Jones

Published On: 22nd Nov 2017 - Last modified: 15th Jul 2024
Read more about - Call Centre Management, , , , ,

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  • In some outsourced environments, included in the service level calculation is the contracted volume of calls vs the actual volume routed during that interval. If the calls routed are above the contracted volume, the SL target may be missed and possibly impact subsequent intervals. This would therefore need to be considered in the SL calculation.

    Sello Moseki 22 Jan at 17:32
  • Sello,

    Agree with you in principal but…

    This should only be used as a measure between the contact centre and client. The actual customer experience is (or should be) a separate measure you track at the same time.

    I have worked contracts where up to 10% variance from the client forecast keeps the SL target, but, should
    the variance go over 10% the ‘best endeavours’ principal applies.



    Dave Appleby 23 Jan at 13:10
  • Hi,

    I disagree with your comments around the abandoned calls that shouldn’t be ignored.

    If I have a 90/30, and a call is abandoned after 11 seconds, why should the SL be penalised? I still had 19 seconds to answer that call.

    All calls abandoned before threshold should be ignored.


    Luc Denis 25 Mar at 19:03
  • Including abandoned calls is right.

    The service level should look at the 90% of calls answered in 30 seconds. The call abandoned so you didn’t answer it. Had you got there in 10 seconds it would not have abandoned.

    jonty pearce 26 Mar at 16:22
  • Is there a way to compute for the SL projection for a day or future dates with the following information available?

    Required FTE
    Scheduled FTE
    Call Volume Forecast
    AHT Forecast
    Actual Planned Shrinkage

    Mark 1 Oct at 04:29
  • For Different LOBs:

    (Ans within threshold)/(Total Offered)*100

    Kaushik 19 Dec at 08:53
  • Old thread now but I disagree with the principle of including abandoned calls depending on your Service Level Agreement.

    If you have SLAs for 80/20 answer rate and say a within 4% abandon call rate then including abandoned calls means you are penalising twice for each abandoned call.

    Abandoned calls should be penalised under a ACR agreement and 80/20 then applies to 80% of answered calls being answered in 20 seconds…or at the very least exclude those that abandoned under the threshold. Otherwise you could have 10 calls offered, 5 of them abandon in 5 seconds and you are instantly saying that you only answered 50% of the calls in 20 seconds where as if they had held on for an extra 10 seconds all of those could have been answered.

    James 7 Apr at 13:35
  • Old thread but for people who are saying that abandoned should be ignored because some calls are getting abandoned before the threshold. Calls getting abandoned before the threshold are called as short abandoned and they don’t impact your SL in any ways. If calculated properly, It helps boost your SL.

    Service Level = {(Total calls answered within threshold +calls abandoned within a shorter amount of time than the threshold)/(total calls answered + total calls abandoned)} * 100%

    Abu 1 Sep at 00:35
  • I came across a statement that the SLAs should be calculated only for the calls inside the opening hours (all calls coming outside the office hours should be ignored).

    How do you see that?

    Aya 4 Oct at 09:21
  • In the system that i use, it doesn’t show the offered number but shows what we handled and the Service level equivalent. Is there a way like reverse math to get the total contacts offered?

    Grubber 13 Oct at 23:21
  • I read through several of the comments. We calculate SL in several different ways depending on the contract we have with the client. If they ask for a SL based on ALL calls answered, and since we can track our clients by a variety of ways, we use the IVR containment in that calculation since it is ALL calls. We do exclude calls abandon within SL, and I would actually argue that the contract doesn’t say all the calls you could have answered, as including Abandon. It specifically states % Calls Answered within Threshold. Many of these contracts include a separate measurement for an Abandonment rate. So IF you include the abandons in the over all SL, you are “dinging” yourself twice. It does not make sense to include the abandon calculations in two places. But back to my point, if the contract says “Agent only” then we look at agent only calls and do not include IVR containment/retention in the calculation. So we try and report to our clients based on the contractual, (or our interpretation), of the requirements.

    Mags Temple 29 Nov at 18:09
  • I understand service levels for calls. How do people record their service levels for emails, post, social media etc?

    Daniel 8 Feb at 15:52
  • Service level for emails, post, social media and web chat

    For emails, post, social media and web chat the same basic formula holds

    Service level = [ Number of contacts answered within the service level threshold] / [Number of contacts offered] * 100

    Jonty Pearce 9 Feb at 16:33
  • Our Service level is to answer 80% of the calls in 120 seconds and we are fairly successful in delivering this. Our client satisfaction is 84% overall and satisfaction with the wait time is 77% which aligns with the ICCS CitizensFirst7 findings. We handle about 450 thousand calls annually with about 30 staff and we are open 24/7.
    We include the abandons in service level in a positive way (treat the same as handled in SL). When I look at a sample of our abandons in service level I see that about 40% abandon in the first 15 seconds telling me that we never had a chance to get to them – they probably got a call on the other line or some other distraction came about.
    We have a SL for email of 5 business days but tend to respond within about 1.5-2 days.
    We inherited our targets and calculation and we’ve been audtited a few times over and asked why it is what it is. Thank you all for sharing your information, it will help me in my discussions.
    Take care,

    Kyla 6 Mar at 15:01
  • Is it also correct to establish SL without specify any threshold? Positive and negative effects on measuring it in this way?
    I.e, the formula could be: Service level = [ Number of calls answered / [Number of calls offered] * 100
    Otherwise, how is possibile to identify the right threshold? Does exist a formula? In this case what values need to be considered (ie: agents number, calls forecast, AHT..) Or if a formula doesn’t exist, what are the best practices?

    Fabio 28 Jun at 22:45
  • Including abandoned calls in the Service Level calculation is the right thing to do if you respect your customers. The short call threshold takes into consideration calls that you determine really weren’t valid calls and didn’t give the call center a reasonable chance to answer. I think a reasonable short threshold is 5 to 10 seconds. After that why should anyone be surprised that a customer might reasonably expect to have their call answered with a minimum wait time? Customers don’t know or care what your internal goal is. Excluding abandons that drop before the Service Time is theoretically the same as setting your short call threshold to the same thing as your goal time.

    Most of the opinions expressed that would like to see abandons excluded from the calculation are probably looking at it from the call center point of view and are concerned with what they are being held accountable to. This is not a customer centric approach.

    The Service Level approach described and recommended in the article is taking into consideration the customer experience. By including abandons in the calculation you are better able to see what your customers are experiencing and potentially hearing what they expect.

    Simple example – Business sets a goal of 80% in 60 seconds. If they are offered 100 calls and 99 of them abandon between 30 and 45 seconds in queue and the one remaining call is answered at 65 second what is the resulting Service Level? If you include the abandons you’re looking at a 1% Service Level. If you exclude them, congratulations, you’re at 99%! Now don’t we feel good about ourselves, we exceeded our SL goal! Yes, I’m sure we’ll get around to looking at the abandonment rate separately and we might figure out what our customers are trying to tell us… That they aren’t willing to wait 60 seconds to have their call answered and they’re taking their business elsewhere.

    Even if you’re the only game in town isn’t the whole point of providing a service is to provide a good service that meets your customer’s needs? There are a lot of valid reasons why a center can’t support a more aggressive, customer friendly service level goal. But even if the center can’t do 80% in 30 seconds shouldn’t we really know how what percent of our callers are getting that experience rather than fooling ourselves into believing that we are meeting their needs?

    Chris 4 Aug at 17:51
  • How can I calculate the service level if I have data of call volume and number of headcount? Can I forecast the service level can be achieved?

    Ray 23 Sep at 14:40